ずにはいられない

ずにはいられない expresses a strong, almost involuntary urge to do something. It is used when something causes you to feel an uncontrollable desire or compulsion to act in a particular way. It often conveys emotion, humor, or a strong reaction to a situation. The phrase attaches to a verb in its ない form (the negative form), and then ずにはいられない follows to indicate that you cannot refrain from the action. Typical contexts include reactions to funny, sad, moving, or unexpectedly delightful events. Note that this is more intense and casual than simply saying you want to do something; it implies you are compelled to act.