There were various red flags that meant I should have headed for the hills, but I was vulnerable at the time, and he only upped the ante several years and a child down the line. I will share mine, in the hope that someone may take it on board, and hopefully others will share theirs too.
In no particular order: very early on in our relationship, he would throw a strop for no reason that I could discern, and looking back, still didn't know what had triggered it. I just knew I felt bad afterwards.
He was always unaware of personal space, and would frequently invade mine. Eg in the car, he would suddenly lurch accross me to access the glove box, without any warning. His car, his space.
Subtle undermining tactics. I am very particular about the perfume I wear. Anything else is a bit of waste of money really. He knew this, but would always try to 'convert' me to another one.
There were many others, and things got worse, with lots of EA, some dv, but I am just thinking of the things that had my Twat Detector been working, would have encouraged me to get out before I had emotionally invested. Please feel free to add. I'm sure I shall think of lots of other things later.