shoot blanks

to be infertile and unlikely to impregnate a woman by having sex with her (from a term used to describe the firing a gun loaded with bullets designed not do harm to the target)

She never realized he was shooting blanks until he hesitated about buying condoms. (example of shoot blanks)

by The Rerturn of Light Joker June 06, 2009

turn tail

to run away in fear (and run is often added although this essentially makes it redundant)

Don't turn tail when you have a huge turnout like that.

by The Rerturn of Light Joker September 21, 2008