It was a pop-culture phrase, before R&M used it on their show.
And pop-culture used it the same way that R&M did. It meant roughly "lay it on me" or "show me what you got". All of these phrases have light inuendo to give them spice (if they had no spice, they would never have caught on in the pop culture). But no: R&M did not mean oral sex every time you heard it on the show.