Welcome to the forum!
It seems to me that you have two things going on here:
1) when Shawn gives Tikkie a treat to 'distract' him from biting his clothing so hard that he actually bites his flesh, too, he is, in reality, rewarding a bad behavior.
2) jealousy - because, if this was a completely normal behavior for Tikkie, he would do it to you, too - and he doesn't.
Now, chewing clothes IS, indeed, a normal behavior in parrots (and that's why we all have what we call 'parrot clothes' that are full of holes

) BUT they know very well when they are just grabbing clothes and when they go 'deeper' and grab flesh. Chewing clothes are, mostly, a show of affection (they are preening us) but, when they do it hard and bite the flesh, it's not normal behavior but a subtle (or not so subtle) sign of aggression. I have a male Senegal that attacked me relentlessly for over 3 years (he did it every chance he got and the entire time I was in the birdroom -I still have the scars from his attacks) but, slowly and surely, he became my friend and he does not bite me now (as a matter of fact, he has become almost a Velcro bird because he insists on been on me almost all the time he is outside his cage). Normally, he just talks my ear off and simply rides my shoulder or hangs upside down from my chest closely looking at what I am doing but, in the last couple of weeks, he has taken to 'pecking' my hair and clothes (he grabs a pinch of them in his beak and he quickly pulls hard on them and releases them). But he has been doing it a bit too hard and would, sometimes, end up causing some mild pain because, although one would think that this is just due to the fact that, as I wear just a TShirt or a top made of some other 'light' material, it's an easy thing to end up pinching me or pulling too hard on my hair without meaning to but I know he knows he is doing it too hard.
I also never believed the 'be stoic and don't show pain' when the parrot bites you position. I think it's ridiculous! Parrots are highly intelligent as well as empathetic so, when they cause pain, they know very well what they are doing. In his case, I just go "OWWW! Stop it!" when it happens or "BE CAREFUL!" when he starts gently (because he tends to escalate it). I don't make a big deal of it because I know he is doing it from a bit of sexual frustration (the female Senegal is not 'putting out' and we are in breeding season - he has been chewing up 'nests' and dancing for her but he has, apparently, not 'impressed' her enough

) and that, once he stops producing sexual hormones in a couple of months, he will go back to been gentle. But, if this is something that has been happening for a while or has been escalating, I suggest you:
a) re-evaluate your husbandry because he could be overly-hormonal from an incorrect light schedule and/or diet
b) stop rewarding the bad behavior
c) avoid confrontations
d) redirect the aggression through training and distraction
Let me know if you want me to elaborate on these suggestions.