fuck that shit, ofc its always easier to think then to do, but i can tell you from my experience at partys is that many other people don't care who is out there (if they are making fun u of or anyone else) cuz most people also won't care about you even when you think they might be laughing or staring at you.
Maybe the type of partys you go to have a different vibe (cuz i used to go to discos and classy bars and of course people stare alot more) but when you go to a "real party", people are there to have fun and not to see who is there and who isn't and how are they dressed or wtv, at least on the trance and thecno partys i didn't get those stares, also on metal/rock concerts or festivals i've gonne to i don't get that vibe. Besides there is no fun at partys without at least a fat guy, you can be that guy that just doesn't care and wants to have fun and fun will find you believe me!!
Next thing you know you will be wanting to go out instead of stay at home playing games, it won't happen every weekend (for example this weekend i wasn't feeling like going out much so i only went to a café with friends on friday) but if you have fun a couple times you will want more