Known in scientific terms as 'Shampupicus Abushulance". It is when a shower cap is pulled over an unsuspecting victim, who is then squirted with shampoo, and then scrubbed verociously with toilet bowl scrubs. This is known to happen to people who refuse to shower.
"Did you see that Seth kid today? His hair was like a mirror!"
"Yeah, we should totally shampoo ambush him..."
1.a method of shutting somebody up
2.something referred to when somebody's hair is extremely messy and/or greasy.
1.I wish somebody would give her a freaking shampoo ambush about now... she won't shut up!
2.eww that guys hair needs a shampoo ambush PRONTO