Pretty self-explanatory. It's the use of a nametag (typically attached to a lanyard around the neck) for sexual purposes. One may try to be subtle, and move their head around in around to gain sexual gratification from the inanimate object hanging around their neck, and gently graze at their crotches. Although not intended to be, it's an act thats ALL too obvious.
Billy: Oh my goodness! What is Renise doing?!
Sally: It looks like she's having a go with her nametag!
Billy: EWWW...nametag fellatio!