It depends on the locker room and who is in it. At the gym/rec center I go, I generally walk around the with towel in hand or over my head, to dry my air. Few guys react, some will say something to a buddy, after I'm around the corner (as though I can't hear them over the locker rows). There are a few guys that have/had a hard time (literally), in the showers.

It happened four times, twice in college and twice since, that I've had sex with some one in the locker room. The last time was the first time with my girlfriend. Always at the end of the day, the first three times was with an employee of the gym/center. More likely was catching someone's eye and then going to her, his, their, my or our place.