It began as a casual Friday night, and ended in near warfare between my girlfriends and me – and all because of a guy.

You’d think we were old enough to know better. Instead, we descended into scheming and snipping. When it was all over, I was left with this question: What’s the etiquette when you and your mates all start hitting on the same man?

The evening started in my apartment. My roomies, Sacha and Suzy, were in their pajamas, settling in to watch a video. Fiona and I were getting dolled up for a party in TriBeCa.

Just as we were about to leave, in walked the Italian architect who’s been sleeping on our sofa to help us cover the rent. With him was a 6-foot tall, blue- eyed, black-haired demi-god.

Suzy’s hand stopped midway from pulling “A Knight’s Tale” from its box. Sacha dropped the bag of extra-butter popcorn she was tipping into a bowl. Fiona cut short a story about her lust interest from the local Cuban restaurant, and I flung away my makeup and launched myself seductively onto the couch.

“Hey, guys, this is my friend Tom from work,” said the Italian. “We’re going over to the Lions’ Den to watch a band.”

“Hey,” said Tom, running his hand through his hair like a roguish Johnny Depp.

“Band?” inquired Fiona casually.

“It’s punk indie-rock – friends from my old art college here,” replied Tom.

So he was gorgeous and artistic. I imagined him painting me.

“Indie-rock! Fab! My favorite,” I lied. “We’ll come too.”

“I thought you were going TriBeCa,” snapped Sacha, who’d slipped her pajama top off one shoulder.

“Oh, that doesn’t start until later,” countered Fiona. We grabbed our coats and hurried Tom out the door.

When we got to the Lion’s Den, on Bleecker Street, our Italian roommate bought some drinks while Fiona and I positioned ourselves on either side of Tom.

We stared at him wide-eyed, bombarding him with questions about art school. But he kept turning toward Fiona. She coyly stirred her vodka and tonic, giggling at his jokes.

I was faced with a dilemma. Should I back off and let her go for it? But then I could be missing my chance.

“Go on Fiona, finish telling us about the bloke in the Cuban restaurant you really like,” I couldn’t help myself saying.

She glared at me.

“Her man’s pushing 50, you know,” I tattled to Tom. I couldn’t stop myself.

“Oh,” said Tom flatly. “Do you girls go for older men?”

It was hard to tell if this was directed at Fiona or me.

“Actually, he’s not my man,” insisted Fiona, still shooting me daggers.

“It’s all about personality, don’t you think?” I offered, trying to hold his twinkling blue eyes with mine.

We stared at each other for a second . . .

“Hi guys,” chirped a familiar voice from behind me.

I looked around and there were Sacha and Suzy in full makeup, pajamas replaced by mini-skirts and boots.

“The film was too cheesy, so here were are!” Sacha announced. “Hey Tom, what’s going on with the band?”

Smiling, he turned to Sach. I was left staring at his back.

At that moment, four hairy rockers burst into the most dreadful din any of us had ever heard.

“Great!” shouted Suzy, above the clamor. She leapt around, doing a bizarre head-banging dance I’d never seen before. Instantly engaged, Tom moved toward her, nodding his head in time.

But Sacha was not to be outdone.

“Yeah, wicked music, fantastic,” she hollered, shimmying after him, attempting a hip wiggle by his side.

Fiona and I were left clutching our drinks, fuming.

The music was terrible, we’d missed our party, and now we were both being ignored.

I couldn’t help feeling cross. The other two showed up just as Fiona and I had been getting somewhere. But then, hadn’t I just tried to cut out Fiona? Weren’t we all being disloyal?

Clearly, there were no firm rules of engagement. If one of us had met this guy first, she would have had a valid claim. But since we were all there when Tom turned up, he was fair game. Still, how were close friends supposed to compete in such a situation? Weren’t we asking for trouble?

Come to think of it, it’s surprising that we haven’t faced this situation before. It’s a well-known fact that New York has an abundance of single women – and a dearth of decent men.

The dilemma has yet to be resolved. After the dreadful band finally finished, Tom disappeared to chat with his college friends, leaving the four of us, and our Italian roommate, to get a cab home.

“Your friend seemed sweet,” I told him.

“Yeah, great guy,” he replied, oblivious to our communal lust. “Actually, I’m meeting him for brunch on Sunday. Come if you like.”

“That would be great!” we all gushed.