The foul smell you that leaks out of your ass from eating foods like Onions and Garlic.
Guy 1: (sniff sniff) Dude what's that smell?

Guy 2: Oh sorry bro my mom made garlic bread two days ago and this Onion Butt won't leave.
by James Hauge February 26, 2009
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A Butt so wrinkly that looks like layers of onions.Marco from AIS has this condition.
Mickael Ghorayeb:Look at marco's sexy onion butt.
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A butt onion is someone that absolutely sucks
Man Jacob’s a Butt Onion
by $@muraibeñdy January 28, 2021
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When a woman has such a delicate ass with a shape such as an onion
Damn, she got dat onion butt, shits finna make me cry
by Onionbutt55 September 16, 2023
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