Wuss Out 

1: v. to fail to participate in something because of moral or social misgivings, or due to lack of courage.

2: v. more polite version of the verb "to puss out"

"I don't know man. What if we get caught?"
"Don't wuss out on me man! Don't you have any balls?"

Wuss Out by VulpinePilot January 8, 2008