1
When something is so plain that you're basically giving it away because your friend is too dumb to see it, and you're too lazy to charge.
'You're telling me you didn't notice the fire? I'll tell you that for free!'
'I'll tell you that for free, you're so thick you could've missed it with a blindfold on.'
'You're gonna pay me for this? I'll tell you that for free, I'm not even trying anymore.'