Or would that be mARRRk your calendARRRs? Here's another early heads-up for Halloween fun: the Pirates vs. Ninjas flash mob event that will occur - briefly - in Jackson Square late in the afternoon of Friday, October 31. (That even leaves time to switch costumes before you head out for the night.) The deal is such: one gang will dress as scurvy sea dogs, the other like silent Asian assassins. They'll assemble (see map) at prescribed points adjacent to the Square at 4:50 p.m. At 5 p.m., they'll rumble like the Jets and the Sharks for exactly two minutes - then, at 5:02 p.m., an air horn will sound and all combatants will disperse. Of course, the whole thing will be immortalized on Youtube. Check for details here and here.