"More people regret Harry Potter tattoos than trans surgeries"

Well numbers are irrelevant, statically only %s count.

So he is essentially saying that more
people who have HP tattoos regret them than more people who have transitioned regret it?

However even when you look at statistics there are always conditions - are we talking transitions that include surgery? Medications? Or we are including someone who dressed a bit masc and used they pronouns for a year before deciding they were just a lesbian but didn’t regret it because “no harm done” etc.

Context is everything but also, don’t debate or argue with someone who relates the gender debate to JK Rowling and Harry Potter. Honestly don’t waste your time.
You’re allowed to have your own opinion on gender ideology, it doesn’t make you a bigot, despite the best intentions to label us that

Apart from asking him to prove his statement I'm sitting here wondering what kind of HP tattoos there are. Is it fancy HP lettering, or a white owl, or a broomstick (quiddich) or that elf? Or is it JKR's face? So many questions... could you ask your friend please OP?

I can’t begin to imagine how you would gather a useful data set of people regretting Harry Potter tattoos that would withstand statistical analysis.

He made the claim, he can provide the evidence. If he can't, he is indeed talking a load of wank and I would tell him so.

Ask him where his data comes from. Sounds like a load of wank to me.

I can suggest a reason why. He knows you're right but doesn't have the integrity to admit it. I hope he is not a close friend. He's just not that bright, is he. Anybody who would believe such a claim is not big on thinking.
A tattoo is also much easier and safer to remove than it is to reverse surgical changes, so it stands to reason people regret cosmetic surgery (of all kinds) more than they regret tattoos.

I dont have data. Does the person youre arguing with?

Tattoos get done on impulse, a lot. Genital surgery and breast surgery does tend to have a longer run-up. So it makes sense to me that regret rates would be much lower.

The fact in particular that regret rates for bilateral mastectomy are so low should make me feel reassured, but I don't feel positive about it for what it says about us as a society, any more than I feel great about breast augmentation and botox being as common as colds.

Past regret rates are, however, based on a past cohort. What the current cohort of young adults will feel a little later on, and in particular what they will call it (probably not 'regret') remains to be seen.