You didn’t waive or assign copyright but you did “grant Y Combinator and its affiliated companies a nonexclusive, worldwide, royalty free, fully paid up, transferable, sublicensable, perpetual, irrevocable license to copy, display, upload, perform, distribute, store, modify and otherwise use your User Content for any Y Combinator-related purpose in any form, medium or technology now known or later developed.”

So, with a license like that, they can legally choose to keep showing your comment if they want to.

That said, I think dang will help delete things if you email to ask and have a good reason. I’ve done it with a couple of my comments.

I did that once and got this reply:

Hi <real name>,

I’m sorry to disappoint, but Hacker News doesn’t delete entire accounts because that would gut the threads it participated in. We do sometimes remove specific comments if users are worried they’ll get in trouble, and we’re also working on the ability to rename accounts. Would either of those help?

Regards,

   <name> (a moderator)

I don’t quite agree with it but have to recognise I have no leverage here.