President Trump greeted supporters with a clenched jaw and double fist pumps as he arrived at a Pennsylvania airport for a 9/11 service — prompting a social media backlash over what many said were inappropriate gestures for the solemn day.

The president, with first lady Melania Trump in tow, clapped his hands and raised his clenched fists skyward as he stepped onto the tarmac at the Johnstown-Cambria County airport in Johnstown and greeted a small group of backers.

“Hey, how are ya! What a good-looking group! What a good-looking group of people!” the president gushed as the crowd cheered.

Others were less charitable.

“It’s the anniversary of one of the worst tragedies in American history – and Donald Trump is PUMPED!!” tweeted Chicago Tribune columnist Rex Huppke.

“I’ve never been as excited for anything as Trump is for 9/11,” added writer Jess Dweck.

“Trump arriving at a 9/11 memorial service this morning. Behold his quiet dignity,” tweeted another writer, Damien Owens.

“Donald Trump first marked the 17th anniversary of the 9/11 attacks with an angry morning tweet about Russia and Hillary Clinton. Now he’s seen fist bumping on his way to the field in Shanksville, PA, where 40 people died after a terror attack was thwarted,” Chris Riotta chimed in.

The president, reading from a teleprompter, later delivered a somber speech hailing the heroes of Flight 93, who fought back against the al Qaeda terrorists who had hijacked their plane, forcing it to crash in a field in nearby Shanksville.