To pop a boner, get an erection, become engorged.
Usually in already awkward situations, like when dancing at a musical rehearsal, in the middle of class, etc.
In extreme cases, referring to the bruise a girl gets when having to come in close contact with said erect penis.

A very smart, pretty, caring, loyal, trustworthy girl. She will never back-stab you and will always give you a shoulder to cry on.

A gay horny notherfucker who has no friends and has wet dreams about his sister. He also can’t say phrases like “let’s go out for a family dinner” since his parents aren’t together because of his dumbass