It's inappropriate to masturbate at work.
Lester is working at his computer, when he starts having amorous thoughts about a coworker and sports an erection.
Lester wants to lose the erection.
Lester focuses on his very non-sexy work and puts the fantasy out of his mind.
Lester gives into his thoughts and starts masturbating at his desk.
The erection goes away on its own, and Lester's day goes on as normal.
Lester's coworkers catch him, and he is immediately fired and has to leave embarrassed while everyone stares at him.