Is it
I might be the worst thing that would have ever happened to you
Or
I might be the worst thing that would have ever had happened to you
These are your best choices:
I might be the worst thing that ever happens to you.
I might be the worst thing that ever happened to you.
I might have been the worst thing that ever happened to you.
fuchsia car 309I might be the worst thing that would have ever happened to you.
Possible, but awkward. I don't advise that you use this.
fuchsia car 309I might be the worst thing that would have ever had happened to you
Impossible.
would have had happened is ungrammatical.
CJ
Comments
Is I might have been the worst thing that had happened to you grammatical?
Yes.
(But it sounds a bit weird to me.)
CJ