shit i had one of those, i just got up and walked out. its usualy ta's not profesers in the labs so there no the brightest. i used to go to the caf, smoke, make calls. i have a freind who has another class thats during part of the lab, he jsut leaves the lab part way to make it.
I don't think TA's give a shit. Its your money you're paying to receive an education. Maybe your lab partner will get pissed, since he has to finish whatever experiment without you being there.
I always just walked out of lab and ate. If you have to tell your teacher you have diabetes and must eat every 3 hours to maintain blood sugar. Never had to tell a prof that but if one sweated me about my eating or leaving class I was prepared to say that. Should work. Bro, but fuck the lab rules what are they going to do send you to detention. I used to drink water while in lab, i just kept my bottle in a bag.