The Jacksonville Jaguars star saw some video of the Buffalo Bills QB taking his first snaps during minicamp ... and decided to weigh in with some friendly trash talk.

"That's a pick waiting to happen," Ramsey posted in a response to the Buffalo Bills tweet.

But within minutes, Ramsey decided to pull back ... and deleted the tweet -- replacing it with another comment, "imma chill."

Ramsey will get a chance to back up his twitter talk when the Jaguars play the Bills during the regular season on November 25.

Meanwhile, Allen got some 1-on-1 time with Bills legend Jim Kelly ... who came down to the training camp to impart some wisdom on the rookie.

The two posed for pics in front of the media before heading to the locker room for a private conversation.

Props to Kelly who seems to be in great spirits while recovering from a major surgery to remove cancer from his jaw.