We have a Dance Production show in the spring that is one of the most popularly attended events on campus. Greek life is not a huge thing on campus, but there are 7 fraternity/sororities (I think?). They're not really typical greek associations though, in that it's not like there's a frat with a bunch of meat-heads who party all the time or a sorority with all the really wealthy, elite girls. I'm on the ultimate frisbee team, which is pretty low key, but we get to go to tournaments on a couple of weekends a year. For example, we went to Las Vegas, San Diego, and UCLA for tournaments this year. More people close their doors than leave them open, but people are friendly in the bathrooms and common rooms. Athletic events aren't a huge thing on campus, but the football and basketball games are probably most popular. We have a lot of guest speakers on campus that vary in a attendence. Chances are though, that there will be at least a couple of speakers each year that really interest you, if not more. There are plays put on at the end of each semester that I would say most of the student body attend.
There are a good amount of couples on campus. Probably more people are into relationships than just hookups, but there's some of both.
I met my closest friends either in my freshman dorm or through people I knew in my freshman dorm. Oxy had a program where all of the people in your freshman seminar class live in your dorm, so it was really easy to get to know people and do homework together. They don't do this program any more, because all of the freshman live togeth now, but that also makes it easy to meet people.
If I'm awak at 2am on a Tuesday, I'm usually doing homework or trying to find a ride to go get some food. The most popular late-night snack around campus are the taco trucks down the street. There are 5 or 6 trucks that park on the side of the road from 7pm to 3am every night and they sell amazing, cheap mexican food. 21 Choices is also a popular snack place, but it closes at 11.
Most people party 1-2 nights a week, generally on the weekends. On Friday and Saturday nights, you can almost always find a party to go to, but there's also tons of stuff to do, both off campus and on, that don't involve partying. For example, last weekend on Friday night I went to a movie and then got back and went to a party off campus with some friends, and then on Saturday I had an intramural soccer game, went to Medieval Times for a friends birthday, then went to a party for him that night.
If you don't want to drink on a Saturday night, you can go to Old Town Pasadena to go shopping or out to dinner or to the movies, there are concerts both on and off campus a lot of the time, there are dances and events on campus, and there's always a lot going on in the LA area if you want to get off campus.