noun: a same-sex friendship that should basically be considered a relationship because the individuals spend all of their free time together. Eventually flack macagins begin to wear the same outfits and shoes, share soup, have sleepovers regularly, wear their hair the same, get friendship bracelets, etc.
Flack macagins can also be a threesome friendship as well, for there is no set limit. Flack macagins' names eventually morph into one as time goes by. For example, john+frank= jank, lisa+hannah+julia= lannalia
"Omg did you see how they wore the same shirt the other day. I mean really, we're in high school, I think that was cool when we were 5."
"Yeah, but its no big deal anymore, they are just flack macagins, its what they do."