A guy who is not a blood relative therefore there is no risk of genetic mutations
Lucy is stuck in the sink cabinet and starts yelling for help. Ashton, her step bro, runs to the bathroom to see what all the yelling is about. He sees that his step sister is stuck, but in the position that she’s in, he notices that she’s got cake. Lucy was only wearing a blouse and short skirt with a very visible black lace thong. Ashton grabs her booty and massages it with his fingers. He then lowers the skirt, plays with the thong, and shoves his finger up her entering. Lucy lets out a loud yelp. “WhAt ArE yOu DoInG sTeP bRo?” She says. Ashton lowers her thong and starts playing with her clitoris with his left hand while jacking off with his right hand. Lucy is moaning in pleasure and suddenly, her insides feel like they exploded as her step bro pounds her. Lucy says in between her moans, “Did you use protection?” Ashton replies, “no risk of genetic mutation here” Ashton continues to pound her until the cabinet breaks and Lucy is now free.
by DaddyMints July 22, 2020
A Pervy boy who likes to watch his sister master bate. When she catches him he fucks her to keep her quiet. They are usually scrawny and have a finely trimmed bush
Girl: What are u doing Step Bro
Boy: I’ll do anything to keep you quiet.

30 minutes later
by MCALHWS February 7, 2019
C’mon mane! We all know why you searched this up!

A Step Bro is a person that all straight men can respect, but don’t wish to be. The Step Bro usually is asked for help by his Step Sis, however, he does a bit more than just help.
His body is usually scrawny, due to the majority of his time going into gaming, and his lack of physical strength makes his appearance rather “unpleasant”. But oddly enough, he is packing somewhere around 6-10 inches. “Like he’s ever going to get a chick?” That statement is beyond wrong! His chick IS his Step Sis!
Dickie: CuM MeaT Ya NeW STeP SiBLinG, TrEVOr!
Trevor: uh... hi!
Helen: awww yeah! My Step Bro finally came! You look HANDSOME! *lets out a slight moan*
Trevor: *Pulls our a cross* BEGON, WENCH FROM TIMES OF YORE!
Helen: bruh.
by Fagimus February 26, 2021
the guy that step sister gets horny with
Step sis: "Step bro, what are you doing?"
Step bro: "I got stuck."
by The guy he is looking for February 13, 2020
As a tiktok star my self I always shout what you doin step bro
Jane: hey stepbro

Dave: hey step sis ;)
Jane: what you doing step bro

Dave: hold still
*bed shakes*
by Big panini :) March 28, 2019
Step-bro is a spreading disease / mental illnesses that is commonly found on the child app "Pornhub" and steps sisters and steps moms are usually the victims of this deadly disease.
"Step-bro I'm stuck!"

"And that's how I met your mom"
by Mai_Atsumi July 13, 2021