It's cruel I know, but one should never pass up the opportunity to welcome an FNG (... new guy) by taking advantage of their lack of experience.
Twr calls approach at Jhb International (it's name has changed several times, but at least this one had a location in it) and says some guy wants to join VFR, what would I like them to squawk.
I naturally answer 2909.
"ZSABC, squawk 2909"
"But M'am it's too high"
"Ok, squawk 2908"
She didn't find it as amusing as me, I suppose it's also 'cos I bring it up after a few libations, which is after morning shifts, most evenings and weekends.
Also, British Global freighters fly in from time to time, their designator being BGB. Again the Tower FNG asks what their callsign is, and I reply, "It's BUGBEAR". I'm sure you can guess the rest.