the worlds colliding theory is quite simple, many people live they're lives in a similar way:
you have your "independant self" (the guy that tells nasty jokes, swears, hangs with the fellas, and is an all around cool guy)
and then you have "relashionship self" (the guy that does nice things for his lady, leaes the seat down, cooks sometimes. still a cool guy, but a little adjusted)
some have the "family self" (which is just like relationship self, just a little less wussy)
If either of the latter mix with the first, say a girlfriend begins to "hangout" with you and your friends, then it's chaos because the way you act around her was never supposed to be seen by your buddies. Who have every right to make fun of you after that. You no longer have the ability to act like the independant wildman because you're constantly in conflict with the relationship guy.
One of the two will have to suside, and depending on your strength of will, it may be the independat side that suffers.