Many many years ago, my cousin, a gullible young Factory Apprentice, was sent off to a distant corner of the plant, having been told to "ask old Joe for a long weight". Of course, Joe said "Hang on here, while I go and get it". Some two hours later, Joe returns, empty handed, cousin asks him where the long weight is. "You've just had it, mate".... (John, England)
Along similar lines, a list of online April Fools jokes, and the Top 100 April Fool's Hoaxes of All Time (a rerun, but a good one).