I was certain that this word was made up by D&D geeks or the SCA. It doesn't appear in the OED (there is not a smidgen of weaponry listed under earspoon), no etymology is given on any of the usual reference sites, and the articles that exist are brief and barren of details. But no, there really was a Bohemian Earspoon. And this is its story.
A Bohemian is, quite simply, a person from Bohemia. Today we call Bohemia the Czech Republic, but whatever you call it, it has always shared a border with Germany. For centuries the two have engaged in battle, or at least shared nasty glances across the border. In the early 1400s the strife was great indeed, due to religious differences and political infighting. This fighting led to the emergence of slangish German names for many Bohemian weapons -- some of them quite odd.
One weapon that was used by the poor folk of Bohemia was a large club with a knot on the end1, sometimes likened to a shillelagh (the Bohemians have a Celtic heritage). This eventually came to be known among Germans as the Bohemian Earspoon (böhmischer ohrlöffel). The reasons for this name are less than clear to someone who does not speak medieval German, but even today the word löffel is used in a number of idioms relating to death (den Löffel weglegen, literally 'to put the spoon away', means to die) and violence (eine löffeln means 'to hit about the head'). It is also possible that the etymology is related to the fact that the böhmischer ohrlöffel was a spoon-shaped club used for hitting people on the side of the head.
Now comes the confusing part. Another weapon that appeared during this time was essentially a heavy spear with two additional spikes set at right angles to the spearhead at the base of the head. It could be used for stabbing, for slashing at horse's legs and reins, or when swung like a bat the sideways-facing spikes were very effective at piercing armor. The German name for this weapon was the knebelspiess, the 'toggle spear'2. It is nothing like the farmer's club. It is what we commonly refer to as a Bohemian Earspoon.
There is one connection between the two weapons; knebelspiess may have been first used as a jagdwaffe and a bauernwaffe3, a weapon for the huntsman and the farmer. The 'toggles' referred to in 'toggle spear' may have originated not as spikes per se, but as a peg used to hold the spearhead to the shaft, or alliteratively, to prevent a boar from running up the spear and mauling the hunter. While a soldier would prefer a more refined weapon, a farmhand herding swine or hunting wild boar would not be too picky about the construction of their spear. Both the club and the spear originated as lower-class weapons.
So perhaps the Germans started calling the spear a böhmischer ohrlöffel simply because it didn't really matter much what the peasants were swinging. It is a small step, after all, to generalize 'farmer's club' to 'farmer's spear'. Whether or not this is actually what happened is anyone's guess. Perhaps there is a better reason for calling a spear an earspoon, now lost in the mists of time. Regardless, I would recommend that next time you are discussing medieval weaponry you make a distinction between the Bohemian Shillelagh and the Toggle Spear; 'bohemian earspoon' is simply too broad a term.
1. "die böhmischen bauern trugen früher starke prügel, die unten einen dicken knorren hatten, und wegen ihrer gestalt mit einem ohrlöffel verglichen werden konnten" Quote comes from Deutsches Wörterbuch. I cannot understand the reference to the original source, but it's there for those of you who can navigate German websites.
2. Toggle: "A wooden pin tapering toward both ends..." -- Webster1913.
3. "der knebelspiesz war eine alte jagd- und bauernwaffe..." - From Deutsches Wörterbuch.
German-English Gictionary of Idioms by Hans Schemann, Paul Knight, 1995
A Glossary of the Construction, Decoration, and Use of Arms and Armor by George Cameron Stone, 1999
And many thinks to my favorite German Dictionary.