A "relationtrip" is a fleeting romantic or passionate attachment that occurs specifically during a trip. This can technically be on vacation, but more commonly occurs during summer camp or missions trips. The aforementioned "relationtrips" last typically no more than 3 days after the end of said event. They can most often times be filed under "worst ideas ever".
A boy and a girl will create a "relationtrip" when they meet on the bus/plane on the way to summer camp or at camp itself. They will "date" (see; hold hands/maybe kiss) until the drive home and break up... if not sooner.
Someone so old school Riverside, California that they have lived through both area codes, 909 and 951.
Also a reference to a new school "bro". A reference to basically every guy in Riverside, as distinguished by wearing sleeveless black jerseys, black skater hats, black shorts, lifted trucks with a grenade sticker on it.
That Bro is so "90951", he just got another grenade tattoo on his hand.