Contrary to American definitions refering to female booty...in Australia "Donk" refers to a males cock. Makes for humorous listening to Soulja Boi's song "She Got A Donk".
Sound of instantly erected penis hitting the down side of your office desk in following situations:
1) a hot female colleague has just entered into the officejust to say hello or ask something
2) a male colleague/pal of yours has just sent you a web link with hot pics you really like
1) Oh, dude, Bridget dropped in early today wearing that red miniskirt again... I'm sure she could hear the DONK clearly this time, man!
2) Yesterday Gerard sent me a hot chick link and I really went.....DONK!!!!!