I assigned the letter grades in the way I usually mark student papers. C would be assigned to flags that were just satisfactory, but seriously flawed in some way; B to strong attempts with minor flaws; and A to inspired or advanced work. Anything lower than a C- is a fail: that country would be better off without a flag at all.To recieve an F, a flag had to be so awful that its level of badness was clearly qualitatively different from that of any flag receiving a D. I had to feel that a country receiving an F had really set out to create a genuinely horrible flag, or didn't really know what a flag was.
Best - Gambia (90/100) - "Great design and colour choice. Also represents the geography of the country (without being a map)."
Note: I suppose the author means that the center stripe looks long and narrow like Gambia. Judge for yourselves:
Worst - Northern Mariana Islands (2/100) - "Appears to have been constructed from clip art. Truly awful."