You can also look at forms 8606 Part III (figure the taxable amount from a non-qualified distribution from a Roth IRA) and 5329 Part I (Additional Tax).
In the simple case where you withdraw only up to your contributions, you wind up with nothing on line 25 of Part III of form 8606 - which gets copied over to your 1040, so no tax to pay. Per the instructions, on 5329 line 1, you put this number (0). Zero on lines 2 and 3, and on line 4 10% of zero is zero. So no additional tax either.
https://www.irs.gov/pub/irs-pdf/f5329.pdfhttps://www.irs.gov/pub/irs-pdf/f5329.pdfOf course, none of this will actually help in your argument, because your friend probably doesn't have the desire to go actually look at tax forms, or there would be no argument.