Why are we called "Hams"?
There are at least two explanations for how amateur radios operators came to be called HAM's.
Explanation #1
"Ham: a poor operator. A 'plug.'" That's the definition of the word given in G. M. Dodge's The Telegraph Instructor even before radio. The definition has never changed in wire telegraphy. The first wireless operators were landline telegraphers who left their offices to go to sea or to man the coastal stations. They brought with them their language and much of the tradition of their older profession.
In those early days, spark was king and every station occupied the same wavelength--or, more accurately perhaps, every station occupied the whole spectrum with its broad spark signal. Government stations, ships, coastal stations and the increasingly numerous amateur operators all competed for time and signal supremacy in each other's receivers. Many of the amateur stations were very powerful. Two amateurs, working across town, could effectively jam all the other operators in the area. When this happened, frustrated commercial operators would call the ship whose weaker signals had been blotted out by the amateurs and say "SRI OM THOSE #&$!@ HAMS ARE JAMMING YOU."
Amateurs, possibly unfamiliar with the real meaning of the term, picked it up and applied it to themselves in true "Yankee Doodle" fashion and wore it with pride. As the years advanced, the original meaning has completely disappeared.
Explanation #2
For another answer to the age old question, how did the term "ham" get started Bill WJ2L/4 sends along this article: Written by WA4HLW -
Three turn of the century members of the Harvard Radio Club, Albert S. Hyman, Bob Almy, and Peggie Murray, named their station Hyman-Almy-Murray. When they tired of tapping out such a cumbersome name, they changed it to Hy-AL-MU. About a year later, confusion resulting between signals form amateur wireless HYALMU and a Mexican ship named HYALMO prompted them to condense the name to HAM.
In the days before regulation of radio, amateur operators chose their own frequencies and call letters. Because they had strong signals - some better than commercial stations - interference became a problem. Congress got busy imposing legislation to severely limit amateur activity.
In 1911, Albert Hyman went to Washington to speak out against the controversial Wireless Regulation Bill. He became emotional when he told committee members that the bill would force them to close their little HAM station, since they wouldn't be able to afford the licensing fees and other regulatory expenses.
The bill passed, however, and amateurs and other private stations were restricted to wave lengths that were considered of little value. But nationwide publicity, characterizing the little HAM station as the underdog fighting against government regulations and greedy commercial stations, associated amateurs with the stations's name. The work stuck and now amateur radio operators throughout the world are known simply as "hams".