Teasing my step-brother with farts

I'm home alone with my step-brother, as our step-parents are away. He starts complaining about not being able to go out with his friends and begging me yo let him go for just a bit. But he didn't finish his homework yet and I'm not in the mood to get in trouble cause of him, so I say no. It just so happens that as I reply, I also let a big fart out. And it seems that my weird step-brother secretly loves that, cause he gets all red and a raging boner shows up in his pants. What a freaking weirdo! I can't believe I'm connected to him! And now he even has the guts to ask me to fart some more in his face! I initially say no but eventually accept to do it with my panties on. He starts jerking off and gets so hard so quickly, but he's not gonna get to cum when he wants. He'll only do it when I say so and when my countdown gets to 0.