When two bros simultaneously penetrate both the vagina and anus of a single woman with their wankers, they become Siamese Eskimo Bros. Can also occur when both bros simultaneously insert their wankers into just one of said orifices, although this is much more difficult depending on the size of the talliwhackers and the diameter of the females vagina or anal cavity.
Jeff and Tom sealed their friendship when they double penetrated Sally by running train on her pussy and anus at the same, thus becoming Siamese Eskimo Bros.
When two males acknowledge having been intimate with the same female and remain on good terms, the men are now bonded by having shared the same igloo at one time or another.
This can lead to perks by making the information known to other males who you can network with.
Male 1: "Yea man, I got us a hook up at the show tonight, we don't have to pay cover"
“When two guys have had sex with the same girl, they’re Eskimo Brothers. You have to know what your eskimo family tree is. It’s how you get things done.”