#8: Jason Segel and Alyson Hannigan
Although Alyson Hannigan and Jason Segel portrayed the perfect couple as Lily and Marshall on How I Met Your Mother, there was some initial hesitation off-camera. Hannigan wasn’t thrilled about their kissing scenes—not because of a lack of chemistry but because of Segel’s smoking habit, which she found unbearable.

To address this, Segel imposed a $10 penalty on himself for each cigarette, but the costs quickly added up, pushing him to quit smoking entirely. After kicking the habit, their on-screen dynamic flowed effortlessly. Hannigan’s insistence didn’t just improve their scenes; it also encouraged a positive lifestyle change for Segel.