When it comes to hot sauce, New York usually comes up short. Be it Mexican, Dixie, or Thai, the bad boy of condiments has flourished in many parts of the world, but all you usually find on tables here is Tabasco. So when Mesa Grill's Bobby Flay needs to challenge his taste buds, he stops at Chelsea's Kitchen/Market (218 Eighth Avenue, near 21st Street; 243-4433). The shop stocks 75 varieties of liquid fire, from down-home Cajun sauces to more exotic scorchers from Peru, Bolivia, and Tibet. What you won't find are the hokey varieties that all basically taste alike but try to differentiate themselves with novelty labels about just how napalmlike they think they are. "There are brands out there, like Rectal Rocket," notes Kitchen co-owner Dona Abramson, "but that doesn't sound like something I really want to eat."