There were warnings and nerves and worries from everyone — former golfers, current golfers, even from fans themselves — about what could happen when the Ryder Cup, New York City and the most polarizing personalities all mixed together at Bethpage.

And everything finally boiled over Saturday, when Rory McIlroy shouted an F-bomb in the direction of fans and spectators later ruthlessly hurled heckles, slurs and incessant boos back at McIlroy and Shane Lowry, his afternoon partner. It led to increased security and New York State police for all four of the afternoon groups, as well as increased messages on video boards reminding spectators of a “zero tolerance policy,” PGA of America told The Post in a statement.

Those messages scattered throughout Bethpage Black were promptly booed by fans.

When the fan conduct around the course paired with 11 ½ points for the Europeans and just 4 ½ for the Americans by the evening, Saturday turned into an embarrassing chapter for the Ryder Cup’s Long Island debut.

“We will continue to closely monitor fan behavior and take appropriate action,” PGA of America continued in its statement.

Everything reached a breaking point on the front-nine of the afternoon session. As fans heckled him while lining up a putt on No. 6, McIlroy, still squatting, said he’s “not going to putt until they shut up.” Lowry reportedly had a spectator kicked out, too. McIlroy reportedly faced comments containing homophobic slurs, taunts about his marriage (“Have you patched things up with the Mrs.?”), reminders of his collapse at the U.S. Open last year (“choker” and “remember Pinehurst?”), insensitive chants related to being from Northern Ireland (“Leprechaun” and “take out the Irish trash”) and more, according to Golf Digest. Lowry also faced taunts about his weight, the outlet added.

“When you play an away Ryder Cup, it’s really, really challenging,” McIlroy said, opting to take the high road when asked if fans crossed a line. “It’s not for me to say. People can be their own judge of whether they took it too far or not. I’m just proud of us for being able to win today with what we had to go through.”

It felt as if this tension had been brewing for the last 36 hours. As he walked off the 11th hole Friday afternoon, McIlroy flipped off fans. As a host with a microphone tried to hype up spectators at the first tee before the foursomes Saturday morning, she started a “f–k you, Rory” chant that kept echoing throughout the main grandstand. As his name was booed during introductions, McIlroy spread his arms out and blew a kiss to the fans.

On the 16th hole of foursomes, McIlroy told Team USA fans to “shut the f–k up,” and then he proceeded to silence them anyway. McIlroy paused just before attempting the second shot, turned toward fans nearby and dropped the loud F-bomb. When he eventually connected with the ball, McIlroy sent it to within three feet of the hole — setting up Tommy Fleetwood for the winning putt in their 3&2 victory.

At different points on the four-ball back-nine, fans continued to taunt with “f–k you Rory” or drawn-out “Rorrrrry” lines. When he reached the 15th tee, he simply pointed at the scoreboard. Team USA’s Justin Thomas, in his afternoon group alongside Cameron Young, held up his hands to silence fans before McIlroy attempted a shot at different points, too.

“What I consider crossing the line is personal insults and making sounds when they are trying to hit on their backswings or very close to when they are trying to go into their routines,” Europe captain Luke Donald said. “That did happen a little bit. It’s happened at other Ryder Cups, too.”

Earlier this week, McIlroy said he “probably engaged too much at times” with American fans at Hazeltine in 2016. Five years later, at Whistling Straits, he didn’t engage enough and felt flat as a result. There’s a balance, he said, and through two days at Bethpage, at least, McIlroy hasn’t hesitated to engage when needed.

This time, it seemed to be only fueling him. Then, everything got ugly.

“We knew what we were going to get coming here,” Lowry said. “It was a very tough day. Being out with Rory doesn’t make it any easier. I think he’s getting the brunt of it.”