It's not anger, it's immeasurable pain.

See, cat penises have barbs on them that stab the pussy pussy and keep the male locked in; the pain from this, visible by the female screeching bloody murder, causes the female to instantly ovulate. The pain caused by cat sex also causes the process to last only a few moments, so the male quite literally has to

Have you ever seen how angry cats are while fucking? Imagine the level of anger they would reach if they could masturabate.