I've been to parties with my sister. If I had it my way she'd come to every party with me and I'd go to every party with her. My dream is that we'd become sister socialites.
When my sister and I go to parties together I think we get sillier and a little more sauced than usual. I know that at some point we usually end up going into this mode where we are laughing and we made some joke about our family so, no one else laughs as hard or as long as we do. We can't stop giggling and we don't even know what it is anymore that we are laughing about. It's pretty much like getting high in high school with your best friend.
You know, when the concept of being high is still foreign and fun.
It's hilarious, and we must look like the biggest dweeb wads ever but, it's okay because your sibling doesn't judge you and because you've got that, everyone else can bug off.