Given "reasonable" attactiveness, which varies by individual, then by definition, attraction will happen.

If one of the people are simply asexual (they do exist) then it won't.
Or if one of them can ONLY be stimiluated by certain cues / kinks / whatever, then the attraction won't happen because the key wasn't turned.

But given a random couple of people, both of which are not repulsed by each other, both of which enjoy a range of "normal" sexual stimuli (I'm not going to bother debating normal), then there is absolutely no possibility the guy won't be thinking about sex.

A lot. Every 7 seconds is a reasonable average. Depends on what other distractions there are in the room.

No matter what Ben tells you.