Conflicted about what?
I have no idea what you consider the 'worst'.
I suppose most would consider abusing and killing animals as the worst thing I've done. I've done alot of other things as well, but everyone seems to hate animal abusers more than anything else.
I don't abuse animals anymore though because I don't keep them anymore. I just don't have the patience for them.
Edit: Oh wait, you said to 'someone'.
Well. I don't know. I've done a lot of things to people. I'll say attempted murder.