SexyCheaterDrunkerdBack?

A night out with the boys may get Justin Timberlake in hot water with girlfriend Jessica Biel.

According to an eyewitness, the singer was in party mode at Chelsea hot spot Avenue one recent night.

"Usually Justin is pretty in control, but he was acting pretty crazy," our spy tells Page Six. "He was drinking tequila all night. At one point, he cleared out a little space and started break dancing. He was bumping into people and spilling drinks. It was hilarious."

Our source also says that at one point, Lindsay Lohan, currently off with on-again, off-again girlfriend Samantha Ronson, tried to dance with Timberlake, but "he shooed her away."

But that didn't stop Timberlake from later cozying up to an unidentified brunette partygoer. "It definitely wasn't Jessica," laughs our source. "He was pretty drunk."

Later that night, Lohan ended up posting a thinly veiled message on her Twitter account, "where's jb cheater" — seemingly referring to Timberlake's girlfriend, Biel. The next day, she added, "Why do people cheat?" But she eventually backtracked, claiming that both messages had been sent by someone who'd hacked into her Twitter account.