Many would say that this reputation stretches back to WW2, but I would argue that the reputation of the French for being "bad at war" actually goes back a good ways further, back to 1871, in fact.

Before the Franco-Prussian War of 1871, the French were often considered to have one of the best military forces, if not the best military force in the world, at least on land (the British, of course, having the reputation of dominating the seas.) The upstart Prussians were generally seen as just that; new political contenders which may have to be checked by a more established and powerful nation, such as France herself.

Due to a long series of diplomatic events which provoked the nationalism of the French people, the French absolutely roared for war against Prussia - or more specifically, the relatively new North German Confederation - in order to curb their power and ensure stability in Europe, but more importantly to ensure that France remain the undisputed dominant European power.

However, to cut a long war short, the Franco-Prussian War ended in disaster, with the Germans sweeping through eastern France, thoroughly destroying and humiliating the French army at every turn. In fact, the Germans won so spectacularly that they even besieged Paris, causing a revolution which would actually take over the city for a few months, before a treaty was ultimately signed.

In the aftermath, France lost Alsace-Lorraine, a very important territory for the culture and pride of France. Additionally, their worst fears were realized; the North German Confederation successfully unified with the southern German states, becoming the German Empire. Wilhelm I was crowned as the first true German Emperor.

As a result of this humiliation, France vowed vengeance. Additionally, the British became worried about the Germans' ever-increasing power on the European stage; this would later influence their decision to cull German power in World War One, although that war would ultimately spiral out of control.

And, speaking of World War One, it wasn't exactly a glorious victory for the French. Four years of terrible, brutal fighting, with absurd casualties - especially at the beginning of the war - and more than a few hard-taught lessons. While they did win, the war left a bad taste in the mouth of most participating nations, though none more so than the Germans. Indeed, the Germans had finally gotten a taste of what the French felt like in 1871, though it was far worse.

This, of course, gave rise to Hitler; and in World War Two, the German "blitz" through France in 1940 was completely devastating, perhaps a bleak reminder of their failures in 1871. It certainly looked rather similar.

So, due to their spectacular losses in 1871 and 1940, and perhaps due to their long and drawn-out conflict in World War One, the French gained the reputation of being "bad at war". Do they deserve this reputation? Not really, seeing as they once led the world in war fighting and military strength for quite some time, and as many have gone in-depth about, have won more wars than they've lost.

However, people probably aren't going to stop calling the French surrender-monkeys anytime soon, and that's almost entirely due to the public perception of World War Two.