Some sort of sexual position as stated by Señor Chang and confirmed by Troy from Community.
Señor Chang: Which is actually quite offensive to people familiar with Mexican Halloween as a sexual position.

Troy: *nods head*
by Jre October 30, 2009
A suggestively named fictional sexual position, referenced (often as a joke) in a TV show or movie, which then takes on a life of its own, and is created. A previously successful example is the Venus Butterfly; an unsuccessful example is the Guatemalan Face-hat.
Just put a name, place, or nationality together with any other noun, call it a sexual position, and people will either claim to have done it, or will invent it - Mexican Halloween all over again
by Real Gibson December 8, 2010
Another name for the (fairly uncomfortable) Bermuda Triangle sexual position, so called because the triangle between the woman's arms, her back, and the man's stomach resembles a chip.

A bunch of people saw Community and decided to invent Mexican Halloween online, not realizing that Mexican Halloween is not a sexual act, but a sexual position.
Mexican Halloween is a sexual position.
by British Swingmaster January 9, 2012
A Mexican Halloween is a sexual act. It occurs when a man is having sex with a woman from behind and upon ejaculation, he opens up a can of chili con carne he had hidden earlier, and throws the contents of the can onto the woman's back.

Note: The chili con carne can sometimes be replaced with salsa sauce.
1: Why are you late?

2: I'm sorry, my boyfriend Mexican Halloweened me and I had to clean my back. Some even got on my bed.
by The Messy Mexican Avenger December 19, 2011
The act of dipping your cock and balls in caramel and then having your girlfriend lick it off wearing a Lucha mask.
I asked my woman if she wanted to bob for apples last night. She one-upped me by adding caramel and a Lucha mask. Turns out it was a Mexican Halloween!
by rjwNU1 October 30, 2009
A sexual position in which the man is taking the woman from behind, aka doggie style, while he is wearing a sombrero, she is wearing the Mexican flag tied around her neck and he’s holding like reigns, and he is screaming “¡Andalé!” and she is screaming “¡Bueño!”.
Him with his boys next day at school: “Damn, my back hurts so bad. I Mexican Halloweened my girlfriend real good last night.”

Them: “That makes me hungry for tacos!”
by Ellis Monroe March 23, 2019
Its when a woman is tied up like a pinata and her pussy is stuffed with sucker type candy (jolly ranchers, life savers, etc) and the man beats the woman's pussy with his cock until the candy falls out.
Last night my wife and I tried the Mexican Halloween. Mints add extra excitement for the woman.
by xfactanother November 14, 2009