When you invite a hot girl to a party and she says she is bringing friends. You think she is bringing girls but when she arrives, she brought several guys with her.
John: Yo, Sara's here and she said she's bringing friends.
Steve: I hope they are hot.
Sara: Hey! These are my friends, Mike, Josh, Aaron Trevor and Ryan.
Steve: Dude...She got you with a Brojan Horse.
A brojan horse is when a bro sneaks other bros into a party that they are not invited to. This usually happens through use of the "back door" method while the invited bro distracts the host.
Patrick: Hey dude, you wanna go to Melissa's party tonight, I heard it was gonna be off the hook.
Alex: Naw dude, I can't cause I wasn't invited.
Patrick: No worries, we'll just pull a Brojan Horse.
v. When one invites a girl to party and she says she'll bring some friends, you of course say that they are welcome to come. She fails to inform you that these friends are a bunch of dudes.
I was so excited that Mary was bringing her friends to the party, but she pulled a Brojan Horse on me!
when a bro in an attempt to hook up with a drunk chick and does not have a condom shows her the empty condom box and says that he has one and continues to have un-protected sex
Bro 1: "Dude how was last night?"
Bro 2: "Didn't have a condom"
Bro 1: "So nothing happened?"
Bro 2: "You kidding? I gave her the old bro-jan horse"