tips for not making people extremely uncomfortable:
1) if someone has visible scars or bandages or burns or anything like that, do not ask them what the scars are from, especially not in a public place. that is putting them on the spot and could potentially be terrifying.
2) if someone is recovering from an eating disorder, do not comment on what they're eating, do not comment on how much they're eating, do not comment on how much they weigh. it doesn't matter if it's positive. if you really need to comment, just tell them that they're brave and you love them.
3) if someone flinches away or goes quiet or reacts badly in any way when you tickle/touch/hug them, for the love of god do not make jokes about it and do not continue doing it. just accept that it made them uncomfortable and don't be a d/ck.