Me and Lev made a few funny nicknames.

Cas- The Clumsy Assassin. (R.I.P Karn's rib.)
Ritsu- Anorexic Gymnast.
Hitori- The Polite Beast

Perrin- The Bed on legs. 
Wylde- Wooosh~! (Her blades.)
Garnet - Rough Gem. (For Steven Universe fans. "Gay Space Rock mom.")
Itzel - Shadow Stalker. (He is short and moves quick.)
Karnrad - "Damn, I was two days away from Retirement." (The Rib joke is killing me, but not as much as Cas is killing Karn. I'm sorry!)