Prez, you cannot be serious!

Maybe Trump should dump the pump.

The President sparked widespread backlash on social media after he was photographed with his fists pumping victoriously into the air as he arrived at a 9/11 memorial service, marking the 17th anniversary of the terror attacks.

Trailed by his wife and the First Lady Melania Trump, the President clapped his hands and then thrust both his fists into the air as he stepped onto the tarmac at the Johnstown-Cambria airport in Pennsylvania Tuesday morning.

“What a good-looking group!” Trump told those gathered to meet him on the rainy morning.

Diane Gottsman, a national etiquette expert and founder of the Protocol School in Texas said fist pumps are typically a symbol of celebration or dominance, more common “when you’ve gotten a good account or great news.”

“It does have its place in very informal situations, but never a somber environment,” said Gottsman, who is also the author of “Modern Etiquette for a Better Life.”

She listed sporting events, concerts and group outings with friends as places a bit more fitting for the enthusiastic move. Fist pumps, she added, are not for “when you are conveying a message that is soulful or respectful or serious.”

Trump’s high-energy display later gave way to a somber speech during which he paid respects to the American heroes aboard Flight 93, who fought back against the al Queda terrorists who hijacked their plane. The plane crashed in a field.

The site, he said, marks the “moment when America fought back” as well as the instant “a band of brave patriots turned the tide on our nation’s enemies and joined the immortal ranks of American heroes.”

The White House did not immediately respond to request for comment.