If you know someone who's very charming and a little bit phony, you can call him a smoothie. A smoothie can talk you into loaning him money even if he already owes you some.
You might also call a smoothie a "smooth-talker," someone who's good at getting what he wants using his charisma. Another kind of smoothie is the one you drink through a straw — a milkshake-like drink often made of fruit, ice, milk, or yogurt. The suave guy definition is older, from 1928 college slang, while the blender drink meaning came along in the 1980s.