In Kylie Jenner's defense, it WAS too hot for clothes in Los Angeles on Thursday...

The 18-year-old reality starlet hung out with her boyfriend Tyga, and rather than wearing a skintight dress and heels, she rocked a sports bra and spandex. We would say she was coming from the gym, but a) she seldom goes and b) she's wearing a full face of makeup -- busted!

While Kylie had previously admitted that she's not as much of a workout freak as say, Khloe, the reality star has been better about working on her fitness -- thanks in part to big sister Kourtney. "[She] had her third baby recently, and she is on a workout kick to get her body back," Kyles said in an interview with the New York Times. "She lives up the street, so I’ll join her for a trainer session sometimes. I also started going to this nutritionist because I was having a bad reaction to dairy. I feel like it made me gain a lot of weight. I’ve now cut out dairy, and it’s helping me get back in shape. Every time I get hungry for a snack during the day, I like to have Justin’s Almond Butter packets. It’s easy."

Easy like...