Keenan Allen Sings and Plays Piano After Dissing Le'Veon Bell's Rap Skills

Remember when Le'Veon Bell posted one of his new rap vids, asked people what they thought about it ... and Keenan Allen hit him back with the brutal "this ain't it" response??

Well ... here's Bell's chance to get revenge ... 'cause the L.A. Chargers star posted a video of himself dabbling in music -- singin' a Daniel Caesar song and playing the piano!!

The initial exchange between the 2 NFLers got personal -- with Bell calling Allen a troll, and KA claiming he was just keeping it real.

Now, Allen has posted a video in croonin' to the Caesar and H.E.R. hit, "Best Part" ... while playing the piano himself.

As for Allen's performance, it's not bad though he acknowledges he needs to keep working -- adding the caption, "Practice Makes Perfect."

Plus, that ain't an easy song to sing -- especially with the high notes -- but Allen didn't do a bad job.