Foster Flop is an Australian saying, humorously describing the inability to get an erection after drinking too much beer.

It is comprised of "Foster", as in the famous Australian beer brand Foster's, and "Flop", as in "to fail completely" or "to fall heavily".
Last night after the party I wanted to root her but I Foster flopped.

Too bad you had a Foster Flop, otherwise we could have had sex.
"Did you have sex last night?" "No, I couldn't. I had a Foster Flop."
by MoMaB July 21, 2012
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Australian slang for being too inebriated (drunk,tanked,etc...) to get an erection.
"Jeeze Mate, I could a shagged that sheila last night but got the Fosters Flop at the last minute"

"Fair dinkum, that's a worry!"
by Maur Schtupedschit June 22, 2005
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