I want to say that they are crazy because they did that/something or they do that/something. Is this form correct:
They are crazy for doing that.
1 Answer
The way you have worded it is acceptable:
Those guys skateboarded in San Francisco? They are crazy for doing that!
Oliver asked for more soup? He's crazy for doing that!
However, in some contexts, we can make this more concise (and this would often be considered an improvement):
Those guys skateboarded in San Francisco? That's crazy!
Oliver asked for more soup? That's crazy!
In cases like these, if you say that the acts are crazy, that implies the people are crazy for doing them.
I would guess most natives wouldn't pick up on any difference in meaning between the two wordings.
I would call them crazy for making a suit out of aluminum foil and carrying around seven crosses, holy water, three versions of the Bible