Skipping the flump

When you do something socially unacceptable because you forget that there are people around. This is anything dumb that you would only do when you're alone, except you do it in public for everyone to point and laugh at you.

Scratching your balls in public is an example of skipping the flump

Person 1: Dude, stop scratching your balls in public
Person 2: Sorry, i just skipped the flump