A phrase used, either ironically or seriously, to reserve the front passenger (a.k.a. shotgun) seat of a vehicle for yourself, under the pretense that you deserve to ride shotgun because of your good looks. Girls are more likely to say this than guys, but either sex can use it.
Erin: "Nope, hotty gets the shotty!"
Sean: "WTF? Whatever, but I pick what we listen to."