1. the putative use of the inside of a banana peel as a halucinagenic drug (a 1960's hoax that became connected with an urban legend about a song of a similar name after the debut of the said song, and susequently spawned more hoaxes, sense 2 is likely also linked to the song)

2. Lysergic acid diethylamide, a hallucinogenic drug

3. a five milligram tablet of valium (from the yellow color of the tablet)
I wouldn't waste my time with mellow-yellow if I were you.
by The Return of Light Joker March 21, 2011
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When you're fucking a bitch who is so ugly that you can't get hard, so you pee in her.

see sour puss
I gave that ugly bitch a mellow yellow last night. Then I beat the fuck out of her.
by Rev. Reggie Dingleberry August 18, 2004
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During sex, casually pissing inside a girls beefcave(vagina)
a guy and girl are in the middle of sex and he gives the girl a mellow yellow
by eat my boogers October 15, 2010
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when a guy pisses in another guys ass. Then the guy craps it into a bottle then they both drink it.
Eric loves mellow yellow, jason and him had 2 last night.
by anthony cannizzo March 23, 2005
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Urine that is left to settle in a toilet bowl. Comes from the energy saving saying that goes "if its yellow, let it mellow. if its brown, flush it down."

Not to be confused with Mellow Yellow which was a song by Donovan in the 60's composed when he took the drug Mellow Yellow. Also not to be confused with the drink popularized by Coca Cola.
"Stop leaving yellow mellow in the toilet! The dog drank out of it and licked my face!"
by Isar December 7, 2005
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1. that yellow mellow bitch was completely trippin out.
by Cameleo September 27, 2006
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