I have this theory that single men never have dogs. This is affirmed again and again when I'm strolling with my 12-year-old bulldog and I meet an irresistible labradoodle being walked by a resistible guy, who instantly refers to himself as "we" and, in case I don't get it, mentions his girlfriend. I'm always tempted to point out that his premature ejaculation is presumptuous and retro — how he assumes I can't have a conversation with a member of the opposite sex without trying to ascertain his relationship status. Besides, I'm not exactly bringing my A-game, in a stained T-shirt and leggings, hair piled in a messy bun. But then, when is the right moment to disclose the fact of the significant other?

Recently, at my friend John's birthday party, I was introduced to Bill, an artist who'd just moved into a loft in my neighborhood. He was tall, dark, and hot, laughed at all of my jokes, and was not shy about flirting. Soon enough we were whispering witty sexual innuendo in each other's ears, and before I left, he asked for my number. In the taxi on the way home, I was ecstatic, thinking my extended dry spell was over. "This is how it works," I thought. "You meet someone who likes you and you like them back." A week (full of flirty emails) later, I told John, the birthday boy, that I was smitten. "Bill?" he replied. "He has a girlfriend. Whom he lives with."

Over a pint of Chubby Hubby and original Beverly Hills 90210s on the Soap Network (why try for creativity when you're miserable?), I wondered what was the ideal time frame for such disclosures.

If you ask etiquette coach Patricia Rossi, a significant other should be mentioned within the first 90 seconds of a conversation "so both parties know and are comfortable with their position on the social playing field," she says. Diane Gottsman, founder of the Protocol School of Texas, advises a follow-up question to soften the blow. (Practice with me: "My boyfriend loves the Yankees. Do you like baseball?") Flirting, Gottsman says, "is only harmless when it doesn't hurt anyone — yourself or someone else."

My friend Elisabeth often found herself failing to mention her long-distance boyfriend of several years when talking to men. Like the time a guy at an indie concert bonded with her for an hour over favorite bands. "It was probably a little selfish and cruel to be flirting all night on my end, but I didn't want to shut down his interest in me — sexual or not," she admits. "I think I have a certain amount of need for approval and I want people to think I'm smart and attractive." Which is the more innocuous explanation for the delayed reveal — that your ego needs a little boost. The more insidious reason, of course, is that you're biding your time to see whether it's worth risking your relationship for a romp with a shiny new acquaintance.

Which was probably the case with Bill. He eventually asked me out for a cocktail and I said yes, telling myself that he'd come clean about his girlfriend — or maybe, by now, his ex-girlfriend? But he didn't mention her once, and instead droned on about work problems, then asked me to cover the drinks because he "forgot" his wallet. When I got home, I erased his number from my phone. Failing to mention the girlfriend was annoying enough, but stiffing me on the bill? Deal breaker.

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