Back in the Metro Days....
Ron was flying a trip with "RD," a captain reknown for his unpopularity with FO's. He had a reputation for being rude to FO's, doing things abruptly without saying what he was doing, extreme overcaution alternating with impulsiveness, and just overall weirdness. Ron was a very junior FO when this incident took place, and couldn't avoid flying with RD.
Ron and RD were in the middle of their trip, on a leg from Spokane to Boise. They were at altitude, in cruise, when RD suddenly sat upright and in an alarmed voice, told Ron to "call Lewiston!"
Ron was perplexed at the request, so he asked why. "Because we have to land there!" was the reply, without further explanation. Ron probed further until RD expounded, sort of: "I was bit by a spider last week. I don't feel well!"
Ron was taken aback, but at RD's continued insistence, called Lewiston station. It turned out, however, that there was an airshow taking place and the airport was closed. "Call Pullman, then," RD commanded. Now, they were already past Lewiston; Pullman was an even longer backtrack. Pullman station confirmed that they could handle the diversion, but then Dispatch came on frequency, wanting to know what was going on. RD jumped on the radios: "A member of the crew isn't feeling well." He was very quick to clarify that he wasn't declaring an emergency. Dispatch pressed for the exact nature of the illness, until RD relented:
"I was bit by a spider."
"Well, if it's not an emergency," said the dispatcher, "you'd be able to go past Pullman and land back in Spokane, right?" RD consented.
"Look, Boise is just as close as Spokane," Ron pointed out. "Why don't we just continue and get these people to their destination, and then you can call in sick?" RD steadfastly refused:
"No, we're going back, and that's final."
The moment the engines were shut down in Spokane, RD grabbed his bag and bolted from the airplane, leaving his flabbergasted FO to explain the situation to 19 angry passengers. After that, Ron had to deal with dispatch, crew scheduling, and then the chief pilot, all of whom wanted to know what happened, and where did RD go? The hospital? Ron had no idea: RD hadn't said a word after they turned towards Spokane. It turned out that RD had ran upstairs to jumpseat home on another carrier, without saying a word to anybody, much less a simple sick call.
Of course, the story quickly spread around the airline and only added to RD's notoriety and reputation for weirdness. The story got considerably funnier when another FO who had suffered under RD got the idea of buying a large bag of fake plastic spiders from a hobby store and leaving them wherever RD might encounter them: in his mailbox, in his flight bag, in the cockpit, even in his hat! It continued relentlessly for weeks; RD was absolutely furious. He assumed Ron was behind it and accused him several times; Ron had to beg the prankster to cut it out!
Eventually the notoriety of the "Spider Incident" died out, mainly because RD went on to out-do himself with other exploits.