hm I was so bored at a job sometimes that I was really happy when people came
I could seem like super-cheery but actually it was just good to have some people around...
so, maybe you can observe people or imagine stuff (eg what their lives could be like etc, like book heroines etc or even ask them about their day/life if you have time for this?) or yeah, think about something nice you could do later (eg go for a walk with doggie etc)
if someone from the team teases you, maybe you could try to come up with a few witty comebacks? (It's not always easy, you could try to prepare some in advance?)
My dad (and some other relatives/friends/acquaintances) can be pretty rude too, sometimes you just need to be rude back, and they will even appreciate it?? (= you need to stand up for yourself somewhat) ideally in a friendly way still, or at least respectful
eg if they might comment at your weight/size (They might be jealous yeah!), you could say, 'Heh, there's more of me to love, jealous eh?' or such?
People can sometimes be bored and may just like to tease other people, out of boredom or stupidity/not knowing what else to say etc. (Or there might be slight resentment, if eg their friend didn't get picked for this job or such, which might be good to find out, maybe if there's someone you can talk with you could ask?) Otherwise it may be just 'good-natured' (even if it might be terribly rude), my dad got picked on a lot in the factory... (They were just bored a lot it seems??)
You could find more interesting topics to talk about? (Even if just stuff from gossip magazines/news/TV or such, whatever the others might be interested in?)
If you can get a book on BDD or some counselling (or a support group) on this it would be good too!!
As for bosses wanting super-cheerful people 'all' the time, hm? Maybe he was just 'fishing for compliments', it would be good if you can find some things (or sandwiches/food items) you can genuinely praise? People have different taste in food... Some relatives who run a food biz can also be a bit offended if one doesn't eat something (difficult with food sensitivities), so I just praise what I remember being good!! (& say I wish I could eat it all lol!)
Wish things get better!! (Or you can find a better job too yeah!)
Sometimes people back off a bit if you tell'em you've been going through some rough times, especially if it's something they might understand (eg death of relatives/loved ones etc) It's good to get to know people a bit to see who you can trust with anything like that though... Or you could pretend to be playing a role in a movie?
You do need to balance it with people you can be genuine with... Like us here and other people in RL who might understand? (Other people in customer service might relate too? There are probably customer service support forums too?
)