They fucked with us by:
1) Fighting against weapons inspection in defiance of multiple UN resolutions that people have conveniently forgotten were the TERMS of the cease-fire that ended the original Gulf War. People love to talk about us acting unilaterally but what they forget is that inspections were part of the cease fire that got us off their ass in the first place.
2) Creating the impression that they were sponsoring terrorists. Even if Sadaam wasn't giving these fringe groups money, safe haven and support (and he was) -- he still went out of his way to leave the world with the impression that he was.
3) Creating the impression that he had WMD. He obviously had them... those kurds he gassed before the Gulf War didn't choke on smog. He could have easily complied with inspections and even embarassed the US with a sparkling-clean weapons inspection report. Instead, he obfuscated UN efforts which made totally no sense at all.
And the kurds want their own state anyway. The shiate muslums weren't particularly happy being controlled by the bathe party either. Its not like that place was this homogenious, happy place to begin with.