Mizrahi and his boyfriend Arnold shot Misshapes-style, after the show.Photo: Tim Murphy

If you’re a regular person with a halfway-decent voice, you content yourself with singing in the shower or perhaps a karaoke bender. If you’re celebrity designer Isaac Mizrahi (whose voice is halfway-decent, at best), you sing at Joe’s Pub with a top-notch jazz band before a roomful of adoring fans, as Mizrahi did Friday night. In an iridescent hoodie-cum-windbreaker and a diamond-encrusted ankle bracelet twinkling just above his sandaled foot, Mizrahi opened with “I Believe in You,” squinching up his eyes while warbling the Broadway chestnut. Perched coyly on a stool, he alternated sips between a yerba-mate energy drink and a vermouth. “I have the upper and the downer,” he observed. “Before you know it, I’ll be Judy Garland.”

Well, not exactly, at least in terms of performance caliber. But he did make hilarious small talk, recollecting a phone-sex partner who instructed him, in old-school Brooklynese, to “lick my bools” (that quickly became the evening’s refrain) and telling a loud bottle-blonde up front wearing a $30 Mizrahi-for-Target summer frock, “You’re 47? You don’t look a day over 37 in that dress.” Later, “re-gifting” pieces of tacky swag to the audience, he threw her a ham. Which, really, was his gift to all of us. —Tim Murphy