Any voyeur whom enjoys finding men masturbating in public usually at known cruising areas or by setting a pre-determined location.
Jerker 1: Hey man missed you at the park & Ride. There were so many jerker lurkers hanging today.
Jerker 2: Damn sorry I missed that. Hopefully they will be back tomorrow.
noun
1. A male who lurks in an area with scantily clad women such as a beach or gym while working up a stiffy and subsequently slinking off to the nearest bathroom or broom closet to masturbate.
The lurker jerker on the next elliptical has an erection.