To go out/date someone from another school. Commonly used in same sex schools as a majority of the people there are not homosexuals.Also used in co-ed schools.
Linda has cross-bred with that blond guy from the private school.
Are you going to cross-breed with that guy from St Xaviers.
To swap an engine from a car with an engine that doesn't belong in it.
I'm gonna cross-breed my BMW to a 2JZ Toyota Supra engine.
I cross-bred my BMW with a EJ25 Subaru engine. Which is also called a FAIL