The look works here too. Also when I hear I can't I say then you don't.
If I get an I can't tie my shoes, then I say go get your flip flops or sandals. THis works really well in the winter. :o) THey would usually tie their shoes.
I also say, when I get the I can'ts is, OK you don't get to come and I walk out the door. This drove my daughter nuts and she would run out the door with me trying to tie her shoes, zip her coat, brush her hair, etc.
If she can't reach something and refuses to use the footstool or chair she doesn't get it. If she's thristy and needs a glass, just say "well I guess you'll go thirsty." NO arguments, no emotion, no attention.
In school I get a lot of I can'ts. Right now my son "can't" multiply so we do flashcards every day. If he is a stinker I say OK today we will do just the two's. He usually will ask for something much more challenging. I homeschool, he is in 5th.
Also I do races, Bet you can't tie your shoes faster than mommy. I wear tennis shoes.
Show me how pretty you can make your hair.
Oh and with hair, I am not the nicest hair brusher, My answer to I can't brush my hair was Do you REALLY want Mommy to do it? That always got a no way!!! And they brushed their hair.