Ryan was booed Saturday night while doing a TV interview at the MMA event in the Bank Atlantic Center, the Florida Panthers' home arena. He was smiling when caught making the gesture by a cell phone camera.
"It was stupid and inappropriate," Ryan said. "I wouldn't accept that type of behavior from one of the coaches or players and it's unacceptable from me. I apologize to the Jets organization, the National Football League and NFL fans everywhere."
Ryan led the Jets to the AFC championship game after they went 9-7 during the season to earn a wild card in his first year as an NFL head coach. He made headlines with his confident statements, including saying the Jets should be the favorite to win the Super Bowl when the playoffs began.
He previously had a verbal feud with Miami linebacker Channing Crowder, and deep in Dolphins territory, he was a likely target for boos.
Jets general manager Mike Tannenbaum added the organization will address the matter internally.
"Rex showed extremely poor judgment and his conduct was inappropriate. He knows he was wrong, has apologized and we have accepted his apology," Tannenbaum said in a statement.
Ryan could be subject to a league fine under the NFL's personal conduct policy.