There are two kinds of villains in TV mystery shows. The plausibly sympathetic type and the smirking creep.
Peter Strzok had rehearsed all the lines of the plausibly sympathetic type. The character that James Comey is trying to play. A man so upright that he combs his hair every hour. But Strzok couldn't help that smirk. Every time he clashed with the impotent House Republicans barraging him with questions that he dodged or refused to answer, the smirk crept over his face and into his voice.
And what was meant to be one character became another character.
Public testimony of this kind is a performance. But Strzok couldn't helping letter his inner self, the one we got to know from his texts, slip through. Both slimy and self-righteous, he came out of the closet in moments like this exchange with Louie Gohmert that quickly went viral.
All Strzok needed to do was stick to his 2 lines of defense
1. You can't prove that my bias affected my work
2. As an FBI agent, I'm far too noble to do wrong
But as Gohmert goes after him, the smirk comes out. Because it is personal for him.
Strzok hates Republicans. He hates Trump. And while his career might be a shambles, he's getting personal satisfaction out of sitting there and thwarting them. It's a grave error.
Gowdy, a former prosecutor, and Gohmert, a former judge, understood that weakness and played on it. Just like TV show detectives play on the poor self-control of their suspect.
Strzok, who had done this a thousand times from the other end, lacked the self-control to keep that smirk in check. To play the role written for him. Instead he had to show his contempt which undermined his character defense leaving him with just the tired con's refrain, "You can't prove I did it."
Instead of doing what he needed to do, Strzok grew overly defensive, refused to concede any point, took any opportunity to speechify, interjected, argued and smirked. The boy couldn't help himself. And didn't. He had waited too long to be able to do this. And so he did it.
He went in thinking that he would play his interlocutors. Instead they played on his weaknesses.