Religious differences.
She though she was God's gift to men and I disagreed.
Inability to communicate:
I said, "Tomato".
She said, "shut the fuck up".
Sometimes small mistakes in communication led to big blowups. For example we were at the airport and this well endowed attendant booked our flight. I wanted two tickets to Pittsburgh and I said, "two pickets to titsburgh". We laughed about that but, later at lunch, she wanted to say,
"pass the salt", and it came out as,
"you fucking bastard, you ruined my life!"