"I told you not to open that attachment."
I was recently commissioned to draw a series of cartoons to illustrate an organisation's staff handbook. Here's one of them, it accompanies the section on computers.
The joke here was originally used in a gag cartoon which I sent out as part of an on-spec batch to all the usual magazines. It did not sell, but I always thought it was a fun joke, so I was glad to give it an airing (and get paid for it, of course) in a different context.
Rejected cartoons, or the jokes within them, will often get used somewhere other than the newsstand magazines, so the time spent on them is rarely wasted.
Royston's portfolio website