Backstreet Boys Happy Cinco De Mayo Fans ... Watch Howie Pound Shots!!!
The Backstreet Boys are giving people ideas on how to spend Cinco de Mayo ... showing fans how the guys celebrate -- with a vid of Howie Dorough slamming shots.
The band's official account posted the video Sunday morning ... and, it follows HD's drinking odyssey as he fires down tequila shot after tequila shot at Howie's Guac and Shots.
And, man ... Howie really knows how to hold his liquor -- downing at least eight shots in the sweltering Mexico heat while apparently MCing one of the events.