Where did my bad mood come from?

Today i was in a relatively good mood... i mean i wasn't bouncin off the walls with cheeriness, but i really had nothing to complain about. But then when i got home from work i was suddenly in the WORST mood ever. Maybe it was because i had to go on campus to do a lot of my homework (which so is not the definition of HOMEwork).

But when i got there i didn't want to be bothered, i wanted to pretend i was the only one in the design lab... i tried to keep to myself, had my headphones on and was staring intently at the computer... i thought that was a pretty good indicator of "do not talk to me i'm working here"-ness... but apparently not. A friend, whose name i shall not mention, for some reason lately has been driving me crazy; and for no aparent reason at all... (except for maybe one small incident, but i should be over that by now), came into the lab. Wouldn't have bad if he didn't start out by sneaking up behind me and pushing the lever on my chair so i dropped about a foot. Not cool. So from there i was so not nice. I didn't say much, left it pretty blatent i didn't want to converse and that i didn't even want to make eye contact. So when i'd finally finished enough "home"work i got up to leave and afformentioned friend wants to chat as i leave, was i done? (obviously) was i in a bad mood? (obviously) did i not want to talk about it? (obviously) These are the types of questions i hate. The stupid ones. So maybe i was overly mean to him for no reason.. but when one is in a bad mood why do people insist on pushing buttons???