It means ridiculous and is short for "ridonkulous," but unlike "ridonkulous," saying it won't get you beaten up.
"Yo, this is donk, I was only a minute over my parking meter and I got a ticket!"
"That shit last night was donk, I talked to my shins for three hours"
"That shit last night was donk, I talked to my shins for three hours"
by idiomaddict January 05, 2010