"Robben didn't think the comedy show would effect him so much, but after two jokes his stomach hurt."

It should be "affect." Always plug the meaning of the word into the sentence and see if it makes sense if you're not sure. To affect is to influence or impact. To effect is to bring about or cause to happen. This make sense: "Robben didn't think the comedy show would impact him so much, but after two jokes his stomach hurt." This doesn't make sense: "Robben didn't think the comedy show would bring him about so much, but after two jokes his stomach hurt."