From watching "The League," we're heard the term Eskimo Brothers for dudes who've slept with the same girl. Urban Dictionary, the source for all things slang, likewise defines Eskimo Sisters -- or Pogo Sisters -- as "two women [who] have slept with the same man in their past."
It may go back to a custom in Alaska of "reciprocal spouse exchange, sometimes described as co-marriage," according to the Straight Dope, although, "Even in areas where it was common, many couples did not participate." (Not all Alaska Natives are called Eskimos, and the term can be considered offensive in Canada, so we'll go with "Pogo Sisters" here.)
Some people use the phrase more generally to apply to anyone with whom they've shared a partner, regardless of whether or not they actually slept with said partner. Here's what happens when you unexpectedly find out you've shared more than just shoes with your friends...
You're in complete and utter shock
You weren't expecting this. You didn't have time to mentally prepare for this. I mean, you don't know exactly how you would go about mentally preparing for something like this even if you did have some sort of forewarning, but still -- a heads up would have been nice. You're too surprised to figure out how to appropriately respond or react to this news at first.
You HATE to admit it, but you feel kinda jealous
Even if you didn't like the guy, you still feel a tinyyy pang of jealousy. If your friend was feeling it with him, he must be a cool dude -- so why did you write him off so quickly? Maybe you should've given him more of a chance. You wonder what you might've missed out on. Oh, and you also momentarily freak out about whether or not your Pogo Sister is hotter than you.
You're sorta annoyed
Of all the people, why did your Pogo Sister choose someone YOU were into for, like, 20 minutes that one Saturday night two months ago? Rude.
You pretend to be happy and excited for her if she's your good friend...
"Oh my god, no way! I can't believe you hooked up with him too! That's hilarious!" *internal screaming*
...or things get really awkward really quickly if you don't know each other that well
That moment when you're playing Never Have I Ever and someone says, "Never have I made out with Johnny," and you and this rando you've never met before both put a finger down. Yeah, awk.
You feel even more crappy about your current dry spell
Ugh. Why does she get to have all the fun?
You're secretly curious about the deets
Even if you think you definitely don't want to know the details ... you also kinda do. Was it just as bad for her as it was for you? Or was it just you? Did she do something you didn't? This is why overthinking things is bad.
You eventually become indifferent to the whole situation
Once you're Pogo Sisters with a handful of people, it becomes a whole lot less shocking when a new member is added to the fam.
You brush it off and laugh about it together
If it was a bad hookup for both of you, then you can bond over how terrible it was. If it was an awesome time for both of you, then you can high five. Either way, it's the beginning -- or the continuation -- of a beautiful friendship.
Head over to MTV's It's Your Sex Life for info about sexual health, just so you and your "sisters" don't end up accidentally sharing anything else -- if ya know what I mean.