Explain the lipstick line in Garden State [slight spoiler in OP]

In the movie, when the leader dog is humping Braff’s leg, Natalie Portman says, “Here comes the lipstick.” Can anyone explain this remark to me?

A dog’s erect penis looks like a red lipstick.

That’s my guess, not having seen the movie.

:confused: um, ever own a dog? A male dog? I think I’ll leave to to someone else. :eek:

That’s kind of what I thought, but the dog had been humping for some time, in fact Braff says he thinks the dog is almost finished. Which distracted me from that theory.