The Kelce brothers dedicated nearly half an hour of their "New Heights" podcast on Wednesday to breaking down Jason's wacky behavior on his first trip as a fan to Highmark Stadium ... and it didn't take long for the elder Kelce to explain why he dropped his top in front of the biggest pop star on the planet.

Jason said he wanted to get the full Bills Mafia experience and immerse himself into Buffalo fans' famous "pageantry" ... but he did joke it all almost caused a tiff with his wife, Kylie.

"She was already telling me to be on my best behavior because we were meeting Taylor," Jason said.

Travis' brother, however, then hilariously said, "I was like, 'Kylie, the first day I met you I was blacked-out drunk and fell asleep at the bar. This is part of the charm! This is part of the Jason Kelce charm!' I want to make my best first impression -- this is my best chance."

The good news? Travis said despite Jason spending most of the night near Swift slugging beers without a shirt on ... the "Bad Blood" crooner had no issues with him whatsoever.

"Well," Travis said, "Tay said she absolutely loved you."

Seems most everyone else around Jason did that night, too. You'll recall, after he brought some little girls up to the box to say hi to Swift, fans pleaded with him to join the Bills.