What are the montague and capulet fighting about?

Most wanted to know question, no? (ーー;)

It's not like 2 families would just say "Hey, let's hate each other and pass that hate to our sons and daughters and embed it in them like micro-chips (Whatever they are) so every time they see each other they will draw swords and kill!" (ヽ(；▽；)ノ)

Probably not the case, as funny as it would've been. 

Anyways, think about it. In act 1 scene 1 Tybalt (Capulet)and his men Samson and Gregory try to fight with Abram and Benvolio (Montague) just because Sampson said "Nay, as they dare. I will bite my thumb at them, which is a disgrace to them if they bear it. {he bites his thumb}" (1.4.43 & 44) Meaning he gave Abram the middle finger, or as the book puts it, and act of defiance. Maybe that wasn't a good idea because they fight about 23 lines later. They're smart.
Still, even though they do act like idiots and such maybe they're actually pretty-
No, they're still dumb.(*≧m≦*)They don't realize they're right from wrong making them rash, which isn't actually a good thing.

Anyway, Montague and Capulet still butt heads about things probably because they are at the same social rank.
I mean, they do have the same ranking in the social hierarchy. That's natural, I guess.

All I hope is that Romeo stops acting like an Edward without a Bella (Twilight references okay?? (,,#ﾟДﾟ)) and sucks it up leaves Rosalind (She's ugly ) and falls in love with Juliet already.
God.
Link to lines listed