As many cultural phenomena are generational trends, eating ass has been normalized by Millenials and GenX. Taking a trip down to Mexico means to lick somebody's asshole.
Faded buddy 1: "Eat ass? dude, not me.."
Faded buddy 2: "What's wrong with taking a little trip down to Mexico?"
Me: "After our first date I took her on a trip down to Mexico! And you know what?? We fucked all summer"
(Girl getting back to her table at "Riley's" bar):
Friend: "I saw you come out of the bathroom with that guy... Was he helping you yak?"
Girl: "Nah, he just took me on a little trip down to Mexico!"