<human>: Condense the text into a few key points

I like to annoy my sister quite a lot, we annoy each other and prank each other. I wasn't just trying to be a dick, it's just what we do. I pranked her recently, and today she got revenge. I woke them up early, and splashed some water on them. But, later after my shower, I went downstairs to get a drink. This is where my sister and her friend was. I then began to annoy them. 

What I didn't realize is how angry they got. Her friend trip me up and I fell over. Except, my towel flew away too. They burst out laughing, and her friend called me pale ass. . I put my towel back on, and on my way out, I tripped up again, this time by my own feet. This caused another huge set of laughter, as my behind was revealed to her friend again.  I was in too much shock to see my towel, so I ran for it butt-naked, and just left the room. 

When I came back in, fully dressed, her friend showed me her little finger and said, "Teeny weeny." They both burst out laughing again, and I stayed in the room trying to change the subject.
<bot>: Annoyed sister and her friend, until I tripped over her friend and my towel fell off, twice. I also got called pale ass and teeny weeny