What does poker face means to guys?

Whenever I walk p guys, I'd always here them sing "poker face." (starting from the chorus by lady gaga respectively) Under ordinary cirstance, I'd consider this a mere coincidence but this happened three times already on diffrent occions (this guys weren't even my friends but some random people hanging by the streets or corridors. Except for one guy who was a clmate in a cl. Their age ranges from 20-28 more or less) I'm kindda buffled by these reactions. PS: I'm not wearing revealing clothes. I wear tshirts and skinny jeans (just the "average school wardrobe") which really makes me wonder why???