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1.
hdu
Text shorthand for "how dare you".
Person 1: "Yo mamma is fat."
Person 2: "HDU make a lame 'yo mamma' joke"
by Channel42 October 23, 2007
 
2.
hdu
"short hand" for "How dare you?!"

How
Dare
U (short for "you" because we can't be bothered to write three letters anymore)
"HDU insult my mother's choices?!"
"HDU hate Britney Spears?!"

by cecilia-weasley October 30, 2007
 
3.
hdu
Text shorthand for "how do you"
"This homework is so hard like HDU even."
"HDU get up at 6AM on a Saturday, that's gross."
by pinkandyellowgirl March 04, 2013