Doctor Who: 10 Worst Things The Twelfth Doctor Ever Did
3. The Way He Treated Danny Pink In The Caretaker
A common trait among NuWho Doctors is their distrust of people in the military, something that is often implied to be part of their own guilt for participating in the Time War. However, while distrust is one thing, his treatment of Danny Pink was actively cruel.
Danny is a maths teacher at the school Clara works at, and the two eventually develop a relationship. Danny is also an ex-solider, which the Doctor takes an immediate disliking to when they first meet in the episode The Caretaker.
Even before he knows Danny is Clara's boyfriend, the Doctor is standoffish and rude as he frequently questions Danny's intelligence and ability to teach maths, condescendingly referring to him as PE. Then when he does find out about Clara and Danny's relationship, his attitude is even worse, going from patronising to actively aggressive.
This is all later explained as him thinking Danny isn't good enough to Clara, but that doesn't excuse the way the Doctor treated him. It's possible that if the Doctor had gotten to know Danny they could have bonded over their negative experiences in combat. Unfortunately the two would remain antagonistic towards each other thanks to the Doctor's initial hostility.