People tend to say this when they are experiencing any kind of pain.
Situation 1
A: It hurts
B: You want to stop, babe?
A: No, keep going. I like it.
Situation 2
A: You're such a slut. Fucking pussy.
B: Uhhh it hurts.(smirks)
A: Why are you smiling?
A: It's my kink.