Basically, it happened like this:

• I fell asleep.
• GF tried to nudge me awake.
• I took offense, and said I was going to bed.
• Heard them stop the movie (so that we could all watch it later), and for some reason became more embarrassed and said I had "no interest" in watching the rest, and that they should finish it.
• Girlfriend come to bathroom to ask if I was mad.
• I said, really loud so her brother could hear it, "I just want to go the fuck to bed" and other bitchy things.
• I went to bed, and when GF came to bed, she wanted to talk about it and I was bitchy some more, and her brother heard us and was embarrassed.

tldr; fell asleep during movie and took great offense at other people for it for some reason

tldr; of tldr; I'm an ass.