Well, even though the original question has been (quite thoroughly) answered, I have to add that my gelding has sported a woody on more than one occasion. Only twice, though, has he beat his drum with any witnesses around.
Normally, he’s quite modest (hates sheath cleaning and needs a goodly dose of “happy horse” before he’ll grudgingly submit), but occasionally during grooming (either by me or my mare), his “kickstand” (LOL) comes down. There was the time, though, when his anticipation of a few ginger snaps when I took too long to get them out of the box resulted in quite a show.
As for my mare, my gelding couldn’t care less about her, even when she’s in a raging heat. The other day when I let him out of his stall after breakfast, my in-heat girl immediately sidled over to him, and did the squat, winky thing in his face. When that got no response, she stuck her head down in his sheath area, to which my gelding just switched his tail and walked off. She was so indignant.
I keep telling her that while he may LOOK like he’s got the equipment, he ain’t going to use it, and I swear she’s going to get her head kicked in one of these days.
The most embarrassing time, though, was when my farrier was here (a young, very good-looking guy). I had my gelding tied in the aisle, next to my mare’s stall door. Farrier and I were shooting the breeze when we both looked over to see my mare and gelding “necking” (doing the mutual nipping/grooming thing along each other’s crests). My gelding was obviously enjoying it FAR too much. I could feel my face turning many shades of red. My farrier just laughed and said “oh great, show it off, Big Guy”.
Oh, and I have a cat (neutered when he was a kitten) who, now after 9 years, has created a “special friend” in the form of the edge of his cat bed. The other day, one of my other cats was hacking up a hairball while Mr. HotStuff was humping his bed, and my husband walks through the house saying “Oh, this is just lovely; over here we have a cat “herking up” on the floor, and over there, another is getting his rocks off.”
Animals - you just gotta love 'em.