I have a few.
My current horse, who is now named Tiara, is registered as "Do-It". Really? How do you think of horrible names like that? It says on her pedigree that her sire was named NITty Gritty, and her dam was DOrstat, so I guess that's where they got it, but I'm sure they could have thought of something else! We renamed her Tiara on the car-ride home when we knew we were buying her. I guess Tiara is a bit strange, but we had Teddy and Troya, and kinda wanted to keep the T's!
Then, we have heard of endless stupid names while horse-searching. One horse we tried (that ended very badly) was named Milt. I don't know his registered name, but that's what he was called. Milt. Wow. Apparently, he was named after the owner's Uncle Milt?
Then, we met a Paint gelding named Cookie. Maybe for a mare, but not a gelding!
I can't think of any more now, so, what are some of the strangest/stupidest horse names you've ever heard?