Macklemore -- I've Definitely SPANKED IT on Airplanes

Macklemore knows ... when you can't find a partner to get you into the Mile High Club, ya gotta take matters into your own hands.

The "Thrift Shop" rapper was on his way to catch a flight at LAX last night when we asked if he'd ever thrown a mid-flight bone ... something that's become harder than ever to pull off these days.

Macklemore admitted he'd never actually done the deed with another person ... but revealed he has performed 1st Class service on himself ... in the lavatory, of course.