Words are tools; and like any tools, they can be dangerous if you use them without knowing what you're doing.
The Orange County Register today had a column from Frank Mikadeit describing a flyer that a self-described "conservative Republican" and "traditional Christian" in Texas had printed and sent to about 70,000 households behind the Orange Curtain, supporting a local anti-illegal-immigration candidate for congress. The headline on the flyer was, "Warning: A Vote for Lying Scumbag John Campbell is Hazardous to Your State and County" (emphasis in original)."
Mikadeit telephoned the Texan who issued this charming message, and discovered that the gentleman was purportedly unaware that a "scumbag" is a used condom. The Texan noted that dictionaries list the word as denoting a "despicable person," as indeed many do. Nevertheless, his ignorance of the source of the epithet not only made him a laughingstock in a prominent newspaper, but also embarassed the candidate he touted (who stated he would apologize to his opponent, even though the candidate had nothing to do with the mailing).
A worse fate befell the unnamed subject of an anecdote from an employment discrimination seminar I attended a couple of months ago. A white supervisor, in an effort to sound "hip," decided to emulate that well-known polyglot Snoop Dogg, and respond to a question from his employee by riposting, "F'r shizzle, my nizzle." The employee was African-American. One lawsuit later, the supervisor learned that "nizzle" was a variation on another word with the same number of letters that also begins with "ni" -- one generally not used in polite company. Oops.