Beto O'Rourke Calls Heckler 'Mother F****r' for Laughing at Uvalde Shooting

Beto O'Rourke is done playing nice guy -- especially when it comes to people who laugh about the massacre at Robb Elementary -- shutting one man down with a brash insult.

O'Rourke was at a campaign stop Wednesday in Mineral Wells, Texas ... a town about 260 miles from Uvalde. The Governor-hopeful brought up the shooting that killed 19 students and 2 teachers, railing on AR-15 rifles -- which O'Rourke says have no business being in the hands of civilians.

While Beto was describing how the weapons were designed for warfare, a man in the back of the crowd, who reports say was a supporter of Gov. Greg Abbott, started laughing obnoxiously.

Without a beat, Beto turned, addressed the man and said, "It may be funny to you, mother f****r, but it's not funny to me." The crowd erupted.

Of course, O'Rourke has challenged Abbott and Texas Republicans since the day of the shooting to take action, and create stricter gun laws -- even showing up at a press conference Gov. Abbott held to urge him to do something.