The Fun Hafnium Flag combines the flags of Denmark, the Netherlands, and Hungary. Reason being this element was discovered in Copenhagen, Denmark in 1922 by a scientist from the Netherlands, Dirk Coster, and another from Hungary, Georg von Hevesy.
Hafnium gets its name from the Latin name of Copenhagen, consequently the Danish banner makes up "Haff of the Hafnium" Flag. Coincidentally the flags of the Netherlands can be seen on the fly side, while the Hungarian flag is on the left.
Note that Hafnium is the Latin name for Copenhagen and this element will soon turn 100 in 2022.