1. To blow vastly out of proportion. To exaggerate or stretch the truth so far that you are basically a straight up liar.
2. To lie. Usually not used as a verb but as a interjection. It is mostly used to call someone else out on what you believe to be a lie. The proper way to call boost is to get as close to the liar's face as possible without touching them and scream BOOST. Similar to Bull Shit, but different.
Edward: I totally got laid last night.
Girl 1: We didn't do anything! I swear!
Girl 2: Swerve!! Stop boosting!