A group of men you don't like, namely a collection of irritating cunts. Plural for 'thrush' - colloquially known as a sole male irritating cunt.
Rob: Michael, what's with sawed off shotgun and machete, don't you just have a status update meeting?
Michael: Yeah but it's with the yeastie boys
Rob: I see, here's some Miconazole to add to the weaponry!
a form of internet slang combining the words "yes" and "bestie," the latter of which is commonly used on stan twitter. it is to be used either as an encouragement or as an affirmative, typically in place of the phrase "yes bestie."