Please don't do that sort of thing -- unless you give the candidate a piece of code and specifically ask what could be improved.

But don't expect candidates to spontaneously criticize the interviewer's code. Yeah, I know, you want to work with people who can think critically etc, but at the time of interview you aren't coworkers and aren't on equal footing. Personally, if I as a candidate see you writing code with bad indentation I will conclude either (a) you were making a point about e.g. correctness or efficiency and didn't bother to indent because it's literally throwaway code, so mentioning the indentation would be a distraction; or (b) you and your team don't care about indentation at all.