What it actually means: To injure or kill by electric shock.
What they actually mean: To flounder is to be clumsy and indecisive, flopping around like a fish out of water; to founder is to fill up with water and sink, or figuratively, to fail.
What it actually means: Something that happens contrary to what is typically expected or appropriate. Can apply to language, as when someone sarcastically says something but means the opposite, such as: “Justin Bieber’s pants look great.”
Source – http://www.buzzfeed.com/patricksmith/words-that-dont-mean-what-you-think-they-mean#.vqoZmzdAm