thanks!

I think you know the answer regarding the association.

Regarding the bad-mouthing, it wouldn't come across that way. The buddy exists for you to sort these issues / sh*t you don't want to be made public. Don't say oh it's all this interns fault I can't get things done, ask for their advice about what you can do to mitigate this

It's a short internship, you have to put your priorities above for this short period. When you get your assignment, clarify to your superior who is working on what part, and it'll become clear who put in the effort.

 

Why don't you just handle your own business, stop talking to him and stay a bit later and fix his misstakes before send-off if your name is on it? 

Maybe don't be a loser and hyper focus on what everyone else is doing but instead shift your energy into completing good work and building relationships in the bank so you get a return offer? Have you tried that?