Actually, you don't even need to use a verb here. 我很酷（Wǒ hěn kù）is enough. This is probably something you didn't learn yet. You should think of it as a sort of

Actually, you don't even need to use a verb here. 我很酷（Wǒ hěn kù）is enough. This is probably something you didn't learn yet. You should think of it as a sort of tarzan-talk: "Me very cool!". If you use 是, you actually put on emphasis on the sentence. Like: "You're not cool.", "I AM cool!".