Unreliability in the most basic things: Constantly unprepared, endless excuses, can't keep their word, always shows up late, disheveled, broke and empty handed.
An unwarranted lack of trust.
Subtle at first @@ eye rolls.
Lies. Even a little white one.
Lies.
Avoidance
Verbal abuse.
I've seen too many relationships start with verbal abuse ... Then get worse and become physical abuse ... Then even murder.
Wanting to see my phone to check and see who I've been texting or talking to. Wanting to know every detail of my day so they can keep track of me. Getting angry at inconsequential things. Being clingy. All would be red flags for me.
The biggest one for me is lies. When the Devil lied to Adam and Eve it changed the world. When you lie in a relationship it damages trust, love and stability. Three essential elements that are needed to have any successful relationship.