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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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May 12 Word of the Day
When someone goes to the gym and spends 90% of the time on their phones scrolling through social media
Looks like its thumb day again for Jimmy with his usual routing... 3 sets of 5 snapchat selfies and 10 sets of scrolling through facebook until exhaustion
by Gary br April 02, 2017
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The act of train surfing on the rear of the train often from station to station. This act is commonly practiced by urbexers, eshays and gimps looking for an adrenaline kick.
Hey bro, did you see the video of Josh doing a back on the other day! What a mad cunt!
by KneeTheBarrier October 14, 2019
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An arse valley wank...(not to be mistaken for anal's similar to a tit wank).

The woman lies on her front while her guy sits on the small of her back facing her feet. He pops his penis between her bottom cheeks and squeezes them together...and off he goes!

Lube recommended.
Sam was concerned when Danny asked her for a Backons...but after he'd explained that it wouldn't make her eyes water, she agreed...and actually found it quite pleasurable (she was even able to finish her crossword).
by Miss Smith January 26, 2008
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New way of saying Bacon. If y’all don’t use it I’m sUiNg
via giphy
by softlyminyoongi April 13, 2019
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