In case you haven't noticed, Al Sharpton's been taking a lot of selfies lately ... and it might be because of Donald Trump.

We got the the civil rights leader Wednesday in NYC, and asked what a lot of people have been wondering about him lately -- what up with the selfie game, Al???

He broke it down for us, and the Prez is only part of it. The other part is about that gym life.

As the Rev says ... back up, haters.