Someone who constantly takes a shower or is known to lounge around in their pajamas or bathrobe. Most notably in seen in lazy old army generals.
Martha: Amos, you're such a showerpants!
Amos: Now you're gonna get it. Fall in, sister! Ten hut!!!
Martha: Crazy guy. Lounging around in your pajamas and bathrobe all day. I don't know how you do it.
Amos: But I can't help it. I'm a lazy old showerpants!