The sexual act of shaving your partners head whilst receiving aggressive fellatio and then finishing off by depositing a significant load onto said partner's freshly bald head.

It is important to remember that it only qualifies as a dirty britney if the shaving and the blowjob occur simultaneously and the event is completed with a vast money shot onto the partners head.
That crazy Vegas whore pulled out a razor and insisted that we did a dirty britney when she went down on me. Obviously I obliged with a huge cumshot onto her freshly bald nut.
by J Reno September 28, 2007
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