I'm a blend of pretty much every European ethnicity ever. Czechoslovakian, Polish, German, and Irish are the main ethnicities, but at best that's like 1/16th each.
I'd say I'm jealous, but I find associating oneself with an ethnicity (assuming you're a white American) is a little pretentious. Sure, your grandparents/parents may have been some ethnicity, but unless your family actually celebrates and maintains the culture, claiming you are that ethinicity seems like it would just come off as offensive to those that actually are.