A man & his girfriend have an encounter

A man and his girlfriend are having a sexual encounter.

He asks her to "go downtown" so, with a sigh, she gets on her
knees in front of him and starts peering at his genitals, looking
and tipping her head this way and that, studying the whole
business.

After about five minutes of this, he asked her in a sort of
peeved voice "Well, just what are you doing?"

She said "I'm doing what I always do when I'm downtown with no
money - just looking."