When lo was younger, he sat in his bouncy seat in the bathroom while I showered. Now I sit him on the floor with some toys, and he either plays the whole time, or sometimes cries for a few minutes toward the end of my shower. I'm not concerned about him cryign for a few minutes though, as I know he is safe, and I need to take care of myself too.
If he is being particularly fussy and I know he is going to just cry the whole time, though, I will just put him in the shower with me. He is old enough now that he sits fairly well in the shower, and he likes to splash the water.