When something or someone annoys/bothers a person, usually of African American backround, they "suck their teeth" making a "smh" sound. It's a sound that stands for aggravation and irritation. It is sometimes used as a self-defense mechanism if rejected.
A young man walks up to an attractive young girl asking for her number, she responds with a "no". The young man replies with "smh, you ain't cute anyway!"
by Cockaroach B December 06, 2009