Underwear that has been worn, discarded and then put on again.
He knew it was a mistake to wear back ons on the day of his wedding.

By the smell of things you're wearing back ons again...
by George Evans May 31, 2008
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Thad: Do not go in the bathroom for the next hour!

Chad: Why broseph? The frat party starts in 30 minutes!

Thad: Trust me! Let it air out!

Chad: But why?

Thad: I had to back one in. And it was a healthy one too!

Chad: Huh?

Thad: You know: Dump some trout, Drop the kids off at the pool, Let one rip.

Chad: OK I gotcha. You could have just sent you took a massive dump.
by ZXY&ABC July 15, 2020
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It is a bad day, you finished your project and the wind blew it away. You're so furious and you've to do it all over again. This is what you called "Back to square one"
by Bryan Chan January 21, 2006
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To relieve oneself of carnal desire while experiencing personnel shortages..
To knock one out.
To unwind the clockweights.
The unloading of crew from the submarine.
To furiously masturbate.
"What a darned inopportune time to ring me,I was getting seriously aroused at the sight of J-Lo in this flashdance knockoff music video,and was about to make the beast with one back.....Now fuck off while i av a wank.
by Rich.C June 22, 2006
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