Americans forget that France was basically our only European ally for a very long time, while we fought the British twice. Memories of what happened in WWII, though, remain strong and color American perception. It’s mostly harmless joking based on stereotypes. The French are far more likely to go their own way compared to the British, including in areas of culture, and that annoys some people. Hence, the “freedom fries” kerfuffle during the 2003 Iraq war.