ML, I've definitely been there done that.
Here is what worked for me.
First, the posturing in front of friends - easy child did this to me too, so it's at least partly a typical teen thing.
There are two options here. First, confront in front of the friends. This is highly likely to provoke a meltdown. If you have a Pervasive Developmental Disorder (PDD) child, this is risky. A typical teen can be more easily talked to about this afterwards in privacy; a Pervasive Developmental Disorder (PDD) kid needs immediacy. It's a tough call. A good compromise is to excuse yourselves from the room containing the friend and take difficult child to another room. Make up a pretext if you need to, then make it clear to difficult child (once you have privacy) that you have chosen this mild subterfuge in order to avoid causing difficult child embarrassment; you didn't have to do it this way, you could have dumped it on him and made him lose face. But the public disrespect is NOT cool, and the friend's laughter is likely to be a cover for embarrassment. Again, this can be a tricky thing for a Pervasive Developmental Disorder (PDD) kid to 'get'. Especially one who is not well and likely to be having MORE difficulty than usual, in other aspects of his coping.
In the meantime - cultivate humour. We have used humour as a teaching tool with social skills. difficult child 3 reads comic books a lot then asks me to explain the humour. Constantly. He's had teachers who use humour as a teaching tool and it has been itneresting to see how difficult child 3 has progressed here. Also difficult child 1 before him, whose recall for quips and funny quotes is stupendous. He's also clever at recalling a good quip to use appropriately. difficult child 3 wants to be like his big brother and so is working on tis, as if he is working on his lessons.
Example of you using humour - difficult child says, "C'mon, use your brain."
Your response - "My brain is worn out from trying to cope with you."
OK, if you plan ahead you could do better.
Or difficult child says, "I hate what you cook, it tastes awful."
You say, "Of course it does! Do you think I didn't go to a lot of trouble, just to make it taste this bad? It takes skill to do this! I match my cooking, to your appreciation."
And the follow-through on the cooking - two options. Both require a quiet talking with difficult child.
First, explain to him that (for various reasons) his tate-buds are playing tricks on him. You could even combine this with a scientific experiment on where on the tongue are the various taste sections. Where does the tongue taste sweet, salt, sour, bitter etc. YOu can get info on these online, it can be a fun experiment. Different family members will have different sensitivities to various tastes and possibly mapping his tongue now might give a different map to when his taste has recovered from the allergies. But a tongue map (you do yours too, maybe get difficult child to map anyone else in his life, such as friends) can help him understand better.
Second - make it clear that if he isn't happy with what food is available, he can learn to cook for himself. I went through this with easy child 2/difficult child 2 who I'm increasingly realising 9from the calm in my kitchen these days) was the faddiest of my kids, and the one who drove me spare. She visited on Tuesday, complaining of feelnig sick again (long story, I think I know what is wrong). She only wanted to eat rice and wanted to put butter on it. I suggested she put a smaller piece of pure butter on her rice, instead of a larger dollop of dairy spread. That way, she would get the butter flavour but less fat. However, she complained that the butter I gave her (which is fairly fresh and has remained in the fridge) tasted "off". Her tastes are EXTREMELY sensitive and her father had to finish her rice.
When younger and with friends present, she would have been loud and scathing in her condemnation of my butter-keeping ability. And a lot of this would have been fuelled by her frustration of the moment - she wanted butter with rice and suddenly couldn't eat it because (in her mind) I had failed to prevent the butter from going rancid. Therefore it would be MY fault that she missed out on eating something she had been looking forward to.
I have had to accept that easy child 2/difficult child 2 is extremely sensitive to certain tastes and textures. I thought difficult child 3 was bad - in some ways he is. But we have trained him to at least try certain foods including challenging foods disliked, from time to time. But creamy textures have always been a problem for him, so have certain food groups (such as shellfish) so if I know he doesn't like crab, for example, I also will avoid feeding him prawns, lobster and krill. Identifying what it is about various foods that he dislikes, has been important. Same with his sister.
With food, we had problems when the two main faddy kids had opposing tastes. For example, difficult child 3 hates creamy textures. But his sister would ONLY eat foods which had been pureed to a creamy consistency. No "bits" allowed. I stopped making biscuits because the only inclusions she would permit were choc-chips. Especially no nuts, not in any food. Except cashews, in stir-fries. No stir-fried beef because it tastes "dead". Related meats also had to be eliminated because it tastes similar. But feeding her chicken all the time - "please mum, I've had enoguh chicken, I don't like it any more."
Having to NOT feed the same food on consecutive meals/days has been a problem. I got around it by cooknig in bulk and freezing, and also ensuring multiple meals available, so I could feed one thing to difficult child 3 and another to his sister, without having to expend too much energy at once.
The other aspect of this problem - when one of the kids is extremely impressionable. difficult child 3, hearing his sister say something tasted awful, would refuse to eat it. THAT was a headache!
So to summarise - I try to understand why my kid is so difficult. The sniffing, for example - if it's a stimulant, you can't do a lot about it and it's simply a case of "tolerate it in your brother, because we tolerate a lot of your issues too." But from there - I will try to resolve an apprent impoliteness (especially a public one) discreetly, but make it clear to the child tat I chose to be discreet to help them save face; I didn't have to do that and next time I won't.
And if that fails - then next time, they cop both barrels in front of friends, and I then apologise to the friend for having to witness an unpleasant scene. I will also say to friend, "What would your mother have done/said, if you had been disrespectful to her in front of a friend?"
If necessary, be prepared to ask friend to l eave. Make it clear that friend has done nothing wrong, but difficult child cannot behave appropriately in front of a friend and needs to have friend removed in order to regain self-control.
Be prepared to pull back from this if difficult child rapidly apologises, especially if the apology is in front of the friend.
And if difficult child gets upset at being publicly embarrassed - point out that you had an agreement which he breached. If he insists there was no agreement then choose this moment to say, "I accept tat maybe you don't remember. So now we wipe the slate clean and put it in writing. If you ever do this again, I reserve the right to embarrass you publicly. After all, having you, achild, publicly shame me in front of your firends - it's the same thing and it must not happen."
The aim of all this is to teach the skills which your child will need inthe big wide world - how to 'take the carp' from a more senior person in the workplace, for example, or someone in authority who may or may not be using that authority appropriately. Even if he feels justified, difficult child has to learn when to shut up, and what sort of action to take in the event of perceived injustice.
We are currently working on training difficult child 3 to provide written proposals, instead of the usual method of nagging until we let our guard slip and say something he assumes is agreement. In the workplace he will need to provide a written proposal, for any new equipment he wants purchased.
Raising a Pervasive Developmental Disorder (PDD) kid is a challenge because you can't apply the usual parenting methods. It causes more problems than it solves. But there can be advantages too (thank goodness, or I'd go totally nuts). And they CAN improve, it does get better.
Marg