roommate drama?

So, I live with two other girls. The one girl Amanda, who has been my best friend since 6Th grade, and Liz a girl from my high school, who I barely know (well, i semi-know her now, since I live with her).
Here is a run down of the situation last semester---- For some reason the roommates decided not to talk to me or include me in anything they did. Especially Liz, but Amanda (who is my best friend) would also leave with Liz and not invite me.---- Alright, so I wasn't an angel, I purposely pissed Liz off because I like pressing people's buttons and seeing their reactions to things.
Over winter break I had a break from them, obviously. I came back and things were "normal". They were both talking to me, me and Liz were actually hanging out and things were good. Up until, a few days ago, not sure why.
Liz hasn't spoken a word to me today (which is slightly okay with me) but I think it was because she gets into "moods".
I have had my two other friends over from 630 to 11pm tonight. The whole time she never came out, (which is fine) but.... shouldn't she eat? or at least use the bathroom? My friends are extremely loud, I think the one may need to up her dose on Ritalin, but anyhow... it just... bothers me.
It bothers me because I think a repeat of last semester is in store for me and I have no idea why.
As I always do, I say "sorry for the excessive loudness" to my roommates when my friends leave, But Liz is being extra bitchy.
I just hope she doesn't try the same shit she pulled last semester.
I already told her I would box her once, and I wasn't kidding.