Tell them that the only patriotic measurement unit is a gun, specifically the American M16.
Since there are multiple versions, we use the latest and greatest: the M16A4. It is 39.97 inches long.
That‘s what American distances and lengths are measured in! I‘m 1.9 M16s tall!
After a while we swap M16 for meters, since the M16 is not only 39.97in, but also -quelle surprise!- exactly one meter long.