Which one do you say? Kitty-corner or catty-corner?
I just say diagonally.
Catercorner.
I had no idea that “catty-corner” was a thing.
I’ll join Sigmagirl in the “neither” camp. I say “catercorner” (with the “r” elided), on the rare occasions when I use the term.
In the spirit of compromise, I say kittycatcorner.
I just recently learned a good southern term for the same sentiment, catawampus.
I vote for catawampus, because it’s a lot more fun to say.
Tim
Kitty-corner.
I’ve heard that before, but used to mean “all messed up”. Like “I checked and he’d stuffed them in the bag all catawumpus.”
Correct
I think that normally means crooked, askew, even all f’ed up.
Whereas “kitty-corner” is a specific geometric relationship, and doesn’t connote wrong in any way.
I live on a corner, the house that is over there, not just across that street or the one that is across the other street is the one that is catty-corner to our house.
Another vote for catercorner. Are we not Dopers? 
I pulled some of the google n-gram files recently, and found that in addition to kitty-corner, catty-corner, and cater-corner, there is also cata-corner in use. In addition, because of the ngram set’s issue with hyphens, you also get kittycorner, etc. Oh, and it can be corner, or cornered.
I thought it was people just screwing up a bit when they meant kitty-corner.
I always thought of people who say “kitty-corner” the same way I think of people who say “veggies”.
I’ve never heard anyone say catty-corner. It’s catercorner, but the r is not usually pronounced.
Aha! The pertinent etymology is the Latin “quattuor.”
Before finding this, I had summoned exactly the same two words to explain “catawampus.” 
In other words… in many voices it sounds like “catty-corner.”
Oh, and Catawampus is also a critter. Like a catamount, but more evil and/or mysterious.
It prefers to live in a cave with lots of bats, deep pits, and odd topology.
And I’ve never heard of catty-corner or catercorner until these threads. I’ve only heard (and used) kitty-corner.