Thad has memorized exactly what his father said to him before he was sent to kil Nora.

" The Allens, the West-Allens their team mean nothing to you. They are not your family."

" You are not a human being. You are no different from a replaceable part in a machine. Your live was never yours."

Every time Thad sees his reflection, he  says to himself . " You are not a human being just a part of  Eobard Thawne's machine. "

"To bring him a fortune in sorrow, because you have no soul."

So low on self esteem he snaps at every human being. Considers everything a flaw in his code including quirks, interests and sympathy.