Bryce Harper's wife says Nationals fans went WAY TOO FAR with their heckling Wednesday ... claiming they chirped him about his newborn son -- and called it all "classless."
Harper is Public Enemy No. 1 in Washington after he left the team last season to get a huge payday (13 years, $330 MILLION) with one of the Nats' biggest rivals, the Phillies.
He's heard constant heckling every time he's returned to Washington to play his ex-team ... but in their game Wednesday, he says fans just crossed the line with their smack talk.