Alitalia's miles can expire in as little as 6 months. For example, if you credit miles for a flight taken on December 31, 2012, you've got to use those miles (and all miles earned prior to that) by June 30, 2013. That's bad. The 24 month requirement is in addition to that "all miles expire every 4 years" facet of their program.

How about Aeroméxico's Club Premier?