A dusty cock is the residue, ie. jizz/ pussy juice combo, left over after banging a slam piece. When dry this jizz/pussy juice combo often leaves a white flaky substance also know as "dust".
"There is no way to avoid the dusty cock after a long night of raw dogging a slam piece"
by DePauty February 02, 2010
When one does a line of coke off of another's erect dick.
Yo I got some coke you wana do a dusty cock off of alex.
by ur freshness December 09, 2008