'Def Leppard' Drummer -- One Direction Ripped Us Off BUT ...

British rockers "Def Leppard" claim "One Direction" ripped off one of their biggest hits ... and get this ... they're flattered.

Def's legendary one-armed drummer Rick Allen tells us any fool can hear the similarities between their 1987 hit "Pour Some Sugar On Me" ... and 1D's tune, "Midnight Memories."

Maybe the real reason for calling off the lawyers ... Allen seems to admit he's done to other bands what 1D did to his. Listen to him ... it's hysterical.

Still, we gotta ask ...