Macaulay Culkin and R&B Singer ... Tongues Tied (VIDEO)

Macaulay Culkin was all tongue-in-cheek Tuesday night ... in the cheek of a middle aged R&B singer.

Culkin and his band, The Pizza Underground, were in Billings, MT with R&B singer Har Mar Superstar ... and he was definitely feeling the band's rendition of "Never My Love."

Macaulay was game for bumping, grinding, dipping and some pretty intense face sucking.