Italian slang for "testis". Plural is "coglioni".
Used to actually mean testis, or to say that someone is an idiot, a prick, or to manifest annoiance.
"Un calcio nei coglioni": A kick in the balls (testis)
"Sei un coglione": you are a prick, you are so stupid
"Non mi rompere i coglioni": do not bother me (literally: do not break my balls)