it's just another way of saying "they're a Lesbian" without actually saying it.
guy: "hey, know that chick judy?"
girl: "yea, what about her?"
guy: "word on the street is that she prefers tacos over hotdogs"
girl: "whut? "
guy: "in other words she's a taco muncher"
girl: "ahh, so is she single?"
guy: "seems so"
someone who munches on vagina of a dirty sort
dude, i'm such a taco muncher, my breath stinks from last night. wana sniff?
or
dude, ur such a taco muncher, your breath stinks from last night,
Dustin Wenninger the mexican
That Dustin Wenninger kid out ran the cops when stealing my car that taco muncher. He even on cross country and eating my tacos
Mexican: Hi welcome to the restaurant!
person 1: SHUT UP TACO MUNCHER!
person 2: …
Man, that girl was dirty and I ate her. She made me a taco muncher!