The only answer you could think of as to why Timmy was a bully was that he was insecure.

Which was the case.

You were right; and that set Timmy into a fit of panic, he didn't know he could be figured out so easily.

He was insecure, yet he didn't want anyone to know that. They would view him lesser as a person. So he started to reflect his own insecurities on others by bullying people less capable than him. ﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍ Timmy wasn't one to assault people like you, but you just pushed all the wrong buttons for him.

He couldn't stand it. Before he knew it he had tackled you to the ground, hands on either sides of your head.

"S-Shut the hell up, loser! I am not insecure!!"

It sounded more like he was trying to convince himself that he wasn't insecure. It was an obvious lie. Tears pricked Timmy's eyes in humiliation, still pinning you to the ground in a fit of rage. He didn't want you to tell anyone; so he wouldn't set you free.