I'm with Jeff. How could you ask a question like that? I have some close girl friends (purely platonic) and that would just be weird.
I did have an affair with a co worker some years ago. We mutually ended it and went on are merry ways. It would have to go down in history as one of the few work place hook ups that didn't end in tears. Anyway, at the last Christmas party before I left I had a similar experience to jeffrey. We were all ribbing one girl about her new beau and one of the girls light heartedly asked how big. She replied pretty good but nothing like him (pointing to me). The girl I'd been with just went bright red and disappeared in a big hurry.
While I later felt a bit proud of that, at the time it was very embarassing as the whole group as one looked at me as if I were naked.