Some of these are great

Mostly I just call things by a shorter version of the actual name (eg "falls", "shocks", "pios")
Wehrmacht HT - Kampbus ("combat bus")
Maxim - shopping cart
KV-8 -
Trogdor the Burninator
ISU-152 - Noob cannon
Raketenwerfer - Poop-chan
B4 - real howie
Obersoldaten - Terminators
Upgraded M5 - quad
M5 with 2x flamer engineers - broke-ass KV-8 or Barton Wartruck

T-70 - rolling sniper
Stug E - Stooge
OKW AA Halftrack: Flak track
Major - Patton
Soviet medics: healing ladies
Any kind of infantry: mans
Still, my all-time favorite unit nickname comes from COH1:
Knight's Cross Holders - KFC holders