Terrell Owens -- Accosted by N-Word-Hurling Jackass

Terrell Owens pulled off the impossible -- keeping his cool like a boss while some disgruntled loudmouth hurled n-word after n-word at the NFL star ... and TMZ has the footage.

It all went down in Miami earlier this month when T.O. was posing for pics with some female fans -- and, according to one witness ... the foul mouthed dude started popping off because he thought Terrell snubbed him.