I've been put in this situation a few times over the years, and I've answered it in every way possible and I still haven't found the right answer.
Scenario: girlfriend sees hot girl (walking down the street, on the bus, wherever)
GF: That girl is so pretty. Do you think she's hot?
me: yea, she's hot.
GF: would you **** her?
Now these are responses that I've said.
me: yea.
ex gf 1: WHAAAAT?
___
me: no
ex gf 2: What a liar. You would totally **** her. why can't you be honest with me?
___
me: oh come on, i won't answer that
ex gf 3: so you would **** her. what the **** is wrong with you, aren't i good enough for you blah blah.
what am I supposed to say? I'm screwed no matter what. I hate it when girls pull this crap on me.