The Awkward Yeti

English has an idiom “to have a sweet tooth” if you really like to eat sweet foods/candy/etc and you crave them even when you know you shouldn’t. So this cartoon makes a pun on the “sweet tooth”, for sweet=sweet tasting, leading to the “sweet tooth” idiom, and secondly “sweet” as an endearment with the meaning “nice, pleasant, gentle”.
Hope that helps.