In Weaver's FNaF universe, Bonnie wants Mike's dong is romantically attracted to Mike. This becomes a problem when the way she wants to be with him is to kill him. In other words, she's a psychotic love-struck stalker. I haven't seen a whole lot of the comics myself, but that's what I've gathered.
It was a creepy running-joke at first, but now it has become creepy feels.