• The senior who is only taking this class to graduate
• the underclassman who is really into the subject which no one else really cares about
• the hipster who smells really bad and is very unfriendly
• the girl who texts a lot, gets yelled at by the teacher, but is then really sneaky about it
• the person who is really obviously stoned out of his/her mind
• the teacher, duh.
• the hot guy who girls are checking out
• the hot girl who everyone is checking out
• the person who is overly friendly and makes small talk with people about annoying small talk-y things like weather, the professor, bodily functions etc
• that super awkward person that everyone notices

remember, one of these is probably YOU.