What does it mean when someone says "I have to wash my hair" when you ask them to do something with you?
Either: they don't want to do anything with you , Or: they have to wash their hair.
they have to wash their hair
It's a brush-off, you should be insulted and not invite that person out again.
Maybe they really have to wash their hair? :) I personally never gave that excuse to anyone. I wash my hair when I shower so it can't be used as an excuse.
It's a hackneyed expression, usually conveying that the person is not interested in doing whatever you're asking him/her to do with you.
it means they hate you or couldnt think of a different excuse
They wanna look spiffy before answering your question!