A word used to substitute another word. Yeah can be used when you can't think of a certain word, as a code name for someone, and/or a word when you cant say a word that you want to say.
"You is a lil yeah..."
"Remember dat time when we went to dat yeah wit yeah and he tried to yeah me?!"
Can be used to delay a particularly embarrasing moment or if you're lost for words, like uh.
Can be used to answer an awkward or idiotic comment.
All purpose response to any situation.
Fiorella: Why did you eat my all my damn sushi?
Mike: Yeeaah, about that...
George W. Bush: They misunderestimated me!
Troy: My hair's on fire. AAAARRRRRRRRGGHGHGHGH! My skin is burning!!!
2. To be used after a long period of laughter on a stupid/lame joke.
3. Used to piss someone off after they have spoken.
b) "Washing machines turn me on"
(reply) "hehehehe, hehehe, hehe, he, yeeeeah.."