The act of getting semen in your ear to the point it makes you temporarily deaf;
When an individual does not hear their sexual partner tell them they are about to ejaculate, typically infuriating the recipient of the ejaculation, as the ejaculate was unexpected.
Cum deafness is a real concern to adult film stars, especially bukkake actors.
Monica Lewinsky must have been cum deaf because when Clinton told her he was about to blow she still ended up getting it all over her dress.