How can I stop myself from smiling?

Sounds stupid and weird but for some reason I can't help but smile everytime I see my older cousin like seriously its freaky!! I don't even wanna smile I have a terrible smile... I just know soon its gonna freak him out I mean come on someone just starts smiling at bạn for no reason everytime bạn see eachother!! Well I am just staying here for a few days with my cousins!!