Is Rudy Giuliani eligible to run for President?

It has come to my attention that Rudy Giuliani was knighted for his efforts after the attacks on 9/11. Since the title of "Knight" or "Sir" is one of great importance in England is this a conflict with the Constitution somehow? I was hearing from someone that the U.S. Constitution stipulates that to be eligible you cannot hold any other offices, titles, or accept money from other countries because it would be a conflict of interest. Is this true?