I was all kinds of thrilled when I was ten, and found out the real meaning of defenestrate. I used to think it had something to do with trees, then I found out it actually means this. My childish mind was filled with glee at a handy new word to threaten people with!
Petard, as in “hoist on his own.” My grandmother used to use this phrase a lot and I didn’t get around to looking it up for years and years. I pictured it as being some kind of pole-arm, though this modified a bit when I got a bit older and, ahem, dirty-minded. Boy, was I completely off base.
I like “petard” because, like “petcock,” the root comes from the latin for “fart.”
So when I hear “hoist by his own petard,” although I know what it literally means, I tend to think of someone being brought low by a thunderous fart at the wrong time.
I have a hard time remembering that chartreuse is green, not red, and that vermillion is red, not green.
It doesn’t help that I’m synaesthetic, and can’t help seeing them the wrong way.
Not British, but the two words always go together for me, mainly because of Ngaio Marsh’s book.
I always have difficulty with chartreuse and puce. Puce should be the colour of vomit, I think.
Looks like a nonce word meaning “to move in such a way as to show off one’s amazing ass.”
Pundit for years, I thought it meant a joker or political cartoonist.
silenus, could you link me a definition for Callipygiate? I can’t find it in my hard dictionary, or the one I use on line. I know, my fallibility is showing, but I can’t know everything. 
Giant_Spongess, vermillion just sounds green, like viridian.
The closest I could come to is callipygian. See
Ooh! I remembered one:
The first time I encountered “bibulous,” (in Dickens, I think?) I assumed that it referred to someone who put a lot of stock in the Bible. That led to a bit of confusion until I looked it up.
sanction. Does it mean “allow” or does it mean “punish”? (I wondered, based on how it was used.) So I looked it up. Both…
But when meaning “to adhere”, the past tenses are regular (cleaved) while the other meaning is irregular (cleave, cleft, cleft (or cloven)).
Garrulous surprises me. I sounds like it should mean something akin to “grouchy”, but, IIRC, simply means chatty or talkative.
Caustic humor. This sounds like it should mean cruel humor at the expense of the unfortunate, but I often hear the word used to describe Groucho Marx. Sure he tilted at many sacred cows, just as Chaplin did, but AFAIK the jokes were usually delivered in good fun.