When two separate aspects or
relationships in a persons life collide: your friends (one "world") become friends with your
girlfriend (a separate "world").
Popularized by The Seinfeld episode "the pool guy", in which Georges Costanzas' girlfriend forms her own friendship with Georges'
platonic friend Elaine (Causing Georges' worlds to collide).
Kramer: 'Jerry, don't you see? This world here, this is George's sanctuary. If Susan comes into contact with this world, his world's collide.
You know what happens then?'
<Kramer puts his hands together and makes
explosion sounds that
exemplify what happens when there are worlds colliding>
KRAMER: 'Ka shha shha shha Pkooo!'