Similar to weeaboo. Someone, mexican or non-mexican, that is obsessed with mexican culture or stereotypes, modern or pre-hispanic.
X: Yeah man, the aztecs were the best culture in the planet, I love them so much.
Y: My god, you're such a Mexiboo.
X: Yesterday I used a charro costume and listened to corridos all day long.
Y: Aren't you being a little bit mexiboo?