"Celebration penalties are things you can't have," McAdoo told Jordan Raanan of ESPN.
The display, which drew the ire of Giants owner John Mara, saw Beckham get on all fours and raise one leg as if he was a dog peeing. The celebration resulted in a 15-yard penalty for unsportsmanlike conduct.
Beckham agreed with McAdoo following a private meeting with Mara on Wednesday, telling NFL Network's Kimberly Jones, "You just can't do it. It doesn't need to be done."
McAdoo said such penalties reveal a lack of discipline, and reflect poorly on him as head coach. He added that the Giants have come up with a plan to address any such incidents in the future, according to SportsNet New York's Ralph Vacchiano.
Beckham met with Mara on Wednesday and later said the only part of the celebration he regretted was that it drew a flag.
"Only thing is just causing the penalty for the team," the reeiver said. "That's really it. I don't even know if they knew to call the flag or not because the look of confusion on their face was, 'Do we throw the flag or not?' And then, it was kind of just like, they threw the flag. So, only regret is causing us 15 yards, having to cover a long kickoff. Thankfully, we didn't have any setback from there. Covered the kickoff well."