Malia Obama -- Fails to Blend in at Lollapalooza ... Thanks a Lot, Secret Service

Malia Obama tried to pretend she's just another teenager raging out at Lollapalooza in Chicago -- but her not-so-Secret Servicemen were a dead giveaway.

The 16-year-old was sans Prez Obama or the First Lady ... hanging only with friends -- unlike the Beyonce-Jay Z concert where Michelle Obama chaperoned her.

The pics are pretty funny -- cause the muscle-bound guy in the black Polo shirt definitely does NOT fit in with the rest of the crowd around Malia. Still, he kept her mud-free ... which is more than a lot of the other fans can say.