Jeremy Chengsaid: I'd like jagex to add an option to permanently block all clan invites. I had a bad experience with a clan and don't ever want to repeat it again.
That's akin to hitting the nuclear button over something really petty, which is probably why Jagex doesn't have it as a option. However disabling clan invites where you can tick it on/off? Yeah, that would probably fit the bill. But permanently blocking all clan invites? If you do that you'll never be able to get an invite ever again.
What if you happen to find a clan you click with really well in the future at some point? You won't be able to join it because they'll be unable to send an invite. Which, as I said, is very likely why permanently blocking them isn't a thing - could see a point to a toggleable on/off option though. Although at that point I'll just say why not ignore them, honestly how often do people really spam invites for clans?