Doo
Doo has 2 meanings
Dude
Short form of "dude," which is used when referring to a companion; often used by males as a nickname for other males but females use it as well; surfers are often associated with the word.
Example
Hey doo, what's up?
How well do you know your texting slang?
Shortened form of doo-doo, a juvenile way of describing human or animal excrement; teenagers often use the shortened version.