Suh dude is a very unique way of saying "what's up dude?".
It can also be pronounced "asuh dude".
People often add a laughter before saying "suh dude" so it will be like, "ahahaha SUH DUDE" and the other person will slightly squint their eyes and reply "aha suh dude".
An alternate way of saying "sup dude" but when you're high af. Keep in mind your voice has to sound like you have a penis In your rectum and you have to smoke good weed for the best results.