There are probably 20 different phrases that I use on a daily basis that I stole from a small child at some point. This is one of them.
Can't Want To
When my niece Molly was little (maybe 3 or 4?) she uttered the phrase "I can't want to do that" which immediately ingrained itself in my vocabulary. Ever since, if you ask me to do something that I'd really rather not, you're likely to hear something like "sorry, I can't want to do the dishes." It's not that I won't or refuse to, it's just that I can't seem to summon the desire inside myself to do whatever terrible thing you're asking (generally this applies to dishes, litter box cleaning, getting out of bed, etc.). It's a complete lack of want and dear little Molly got it exactly right.