(n.) A collection of people at some event who don't really belong together as a group. Perhaps you are going out with two friends from different friend circles, and one of your friends brings another friend who you don't even know. Loomgroups are usually really awkward, but can potentially become real groups.
Ugh, I thought I was just hanging out with Bill and Steve, but then Steve brought his camp friend along and Bill brought his girlfriend. I hate loomgroups.
A combination of people, who, if hanging out together, would create an awkward and hilarious group dynamic. This often happens when combining different social circles or worlds doesn't go as smoothly as one would hope.
So dude, last night after you left the party, the people left in the house were me, my mom, my ex-girlfriend, and that Yugoslavian kid who doesn't speak English. What a loomgroup!