J.K. Simmons -- Calling All Cops ... Mi Burrito Es Su Burrito

"Whiplash" star J.K. Simmons went off again -- but instead of throwing chairs ... he was tossing out free Mexican food to cops at his favorite lunch spot.

Fresh off his Oscar win -- for playing a violent hard-ass -- Simmons flipped the script while grabbing lunch Tuesday at Poquito Más in the Valley. We're told he was buying for 2 friends, and got his usual ... a scampi burrito -- but while ordering he saw a couple of LAPD officers in line and picked up their tab too.

Looking to spread even more love ... J.K. stepped up again when a 3rd cop walked into the restaurant.

We're told Simmons dropped about 50 bucks for all six meals -- which makes the moral of this story: Always be generous. Especially when you can get a great deal.