Which of the following examples is ungrammatical?

I ain't hungy.

I am not hungry right now.

I is hungry.

Yo' dog, are you hungry?

The ungrammatical example is I is hungry, which is the third option here. This is ungrammatical because the conjugation of the verb to be is incorrect - I always goes with am, not is, which is used for third person singular only, and I is first person singular. The second example is the only completely acceptable one. The first and fourth examples aren't ungrammatical, but they are colloquial and should not be used in written form.