[quote=The Nexerus]
Haha, what.
[/quote]

Tyrion killing Tywin is out of character. It's a stupid decision. In the book ( I just reread that scene to write this response) you can feel the anger coming from Tyrion after his conversation with Jaime. He states how going to kill his father may end up with him dead. His father's chambers have two dim witted guards, and at one point Tyrion expects them to burst in and kill him but "I'll take one of them with me for sure."

If he had killed Tywin for just being a dick, Joffrey would have died much earlier.