Step-Bro, come in here - I have the best idea... let's have some harmless fun and play "Who's Going To Cum First"! I know it's naughty and we probably shouldn't, but... I'm pretty confident you're going to cum before I do and I'll win. Want to try and prove me wrong?
Let's start with missionary so it's fair for both of us, okay? I love how that feels so I'll push you onto your back and ride you for a while, before you decide to lick me out as you're getting too excited...
I'm going to finish you off by presenting my pussy to you in the doggy position. I can see you close to the edge so I grab your balls, and you unload all of your cum deep inside of me.
Don't feel bad about losing, I knew I was going to win! Let's rematch sometime soon though!