Defenestration has always pissed me off - if you parse it, it should really mean, "to remove one's window"!
On that note, I've always been a fan of words whose etymologies are amusing and obvious to those in the know - words like, say, antediluvian. Literally - before the flood. I.e. really freaking ancient.
Also always enjoy new slang, especially when it fits a niche that previously lacked any sufficient word. For instance, from the world of cs-hackery, words like "hack" (in the original, MIT sense, that is), or "munge", or "frob", or for that matter, "foo" and "bar". Especially when such slang also has amusing etymology - for instance, it's common at my school to refer to anything particularly nasty with the nounal form, "nast". You can have, therefore, things "made out of nast", or "looking like nast", or etc. I've even heard phrases like "liquid nast". And of course, there's a shelf in our dorm that always collects dust and never gets cleaned, so it's been named "the nast shelf".
