The liberation of France, the rest of Occupied Europe, and Germany was extremely destructive, although not quite in the way the joke suggests.
In a 1946 article, "War Damage and Problems of Reconstruction in France, 1940-1945," George Kyte wrote:
Unfortunately for France, the invasion which liberated her brought about more destruction than she had suffered during the victorious onslaught of Hitler's armies in 1914-.
Many cities such as Brest, Caen, Dunkerque, Falaise, and St. Lo were almost completely destroyed. Hundreds of towns, villages, and farms suffered the same fate. All told, over 1,200,000 buildings were demolished or sustained major damage, and more than 1,000,000 people were homeless. Several thousand kilometers of mainline rail track were torn up [mostly by retreating German troops], 2,000 railroad bridges were destroyed [by German demolition, partisan sabotage, and Allied bombing].
This damage was caused by two things:
All in all 1,500 French towns were badly damaged or destroyed.
One of the important things to realize is that the most intense destruction was concentrated in a few areas in France where the fighting was dragged out or the German resistance was especially fierce.
The fighting in Normandy took nearly three months (early June to early August) before a breakout could be achieved. Several of the towns Kyte mentions were destroyed during the fighting for Normand. For example, Norman town like Caen, Bayeux, and St. Lo were caught in intense fighting that lasted for weeks or months. Day after day bombs and artillery shells hit in and around these towns. Caen itself was hit by heavy air raids on June 6th during the D-Day landings and on July 7th prior to the Operation Charnwood breakout efforts.
In September 1944, the key port Le Havre of was heavily bombed by Allied warplanes before Allied troops attacked the city. 5,000 French civilians died in the air raids. The large port of St. Nazaire was "100% destroyed" by Allied bombing and shelling, according to post-war reckonings.
By contrast, the post-breakout race across France was extremely rapid. Between August 1st and September 1st, the U.S Third Army had advanced nearly 350 miles. There was relatively little German resistance and troops spent more time marching and driving than they did fighting and shelling. Many towns in the path of the campaign weren't defended by German troops and so were largely spared. Others were defended, but were quickly encircled and captured. As a result, many of those French towns were somewhat damaged in the sporadic burst of fighting, then passed on without being blown to oblivion.
The destruction elsewhere in Europe followed a similar pattern. In Germany for example, some towns were relatively untouched by the war. While others were the site of intense fighting and bombardment. In WWII, the the city that suffered the most war damage (as a percentage of buildings destroyed) was the German city of Jülich. Sited on the banks of the River Rur, Jülich was a gateway to the strategically-vital Rhineland.
On November, 16th 1944, bombers hit the city and leveled 97% of it. The rest of the city was smashed in the ensuing three months of fighting went on until February 23rd, 1945. The city was eventually rebuilt from the late 1940s to the mid-1950s. The only scars of its past are the craters that have been preserved in a few public areas.
One of the main American strategies in fighting the war was to have as little casualties as possible. Anthony Beevor talks about the effect in his book -"Ardennes 1944: Hitler's Last Gamble"- The strategy was simple, the US high command was very worried about war support, especially coming off the back of isolationism and with Japan being seen as the main and more alien enemy. (Also technically we fired the first shot by dropping depth charges on a German submarine in WWII before war was declared, interesting fact, even though no one cared about it at the time) Anyways-Germany first- was thought to be far better strategically (and was better in hindsight), but had the one problem of keeping up American war support. Therefore, the Americans avoided casualties like the plague, which required overwhelming artillery fire. The fact remains though, enemies usually concentrated around villages, towns, ect, and to take it with minimal casualties meant using artillery to its fullest effect, which meant devastated towns. The "Long Toms" 155mm guns were the standard artillery for the US, and a 155mm gun was the largest standard/mass produced artillery of any nation. There were reports of cows that had been blown up onto the roofs of houses. Also, clearing houses of enemies involves large amounts of explosives like grenades and even rolling artillery right up to the building and shooting into it. Even solely infantry would rip doors off of houses and use them for fox-hole covers. Germans would completely dismantle furniture in homes for firewood and were always desperate for food. Civilian were not just massacred however, during bombardment. By hiding in cellars they avoided the artillery, but everything above them was destroyed, and it was still pretty heavy on the civilian casualties. We also had overwhelming air superiority by this time which allowed deep strikes into enemy territory, we would bomb church towers just to spill the debris onto the road so the Germans could not use it to resupply. Swallows returning to the destroyed towns became confused as to where to nest because all the buildings were destroyed during the Battle of the Bulge. Destruction on the western front was bad for those reasons, but the eastern front had more spread out destruction, but when it happened it was far worse than the western front. Soviets burned everything they retreated from, the Germans dismantled every house they came across, and entire cities were intentionally destroyed.