Pulling a Boris
It means taking someone elses crush. An asshole who goes after his friend's crush and dates her even though he has dibs on her first. Being a total douche bag or dick head.
Dude Josh stop being such an asshole! Stop pulling a Boris! Edward had dibs on her first!
pulled a Boris
To promise something but does not deliver it
John said he was gonna fix my car but he pulled a Boris on me