Over on the excellent Hush-Kit, there is a list of the best looking French aircraft. It's a list that is not without its talking points - like cricket, rugby and football teams, every reader will always see some 'inexplicable omissions' from such selections. Where, for example, is the Latécoère 28 (the floatplane version flown by Jean Mermoz shown previously here)? I must also confess to having a soft spot for the Nieuport-Delage Ni.52/62/72 series, despite the odd sesquiplane 
configuration; and for the Dewoitine D500 and the Blériot-SPAD 510, which both staggered on in service until May 1940. Indeed, all the wartime SPADs have their rugged, business-like, charm, but elegant they are not - not even the more streamlined S.20. You might also include the Caudron C.640, but whilst powerful and streamlined, it remains a knock-off of the DH88 Comet.
But no, we are not here for the best of French aviation, but for the worst - the ugly monsters that should really have never left the designer's drawing board. Goodness knows, there is plenty of choice - the nation that gave the world the Mirage, the Caravelle, and the three on the left, also gave us some slab-sided brutes. So here is a top ten (should that be a bottom ten?) of the worst offenders against aesthetics and aerodynamics (older British readers can start channelling disc-jockey Alan Freeman if they wish, but the selection is not in strict order).
The Sud-Est SE100 was conceived as a day (two-seater) or night (three-seater) fighter. It would be armed with six forward-firing 20mm cannon, a further two in the rear compartment, and a seventh in a ventral hatch. The prototype was captured in 1940.
The five-engined Penhoet-Richard RP2 flying boat, designed for trans-Mediterranean passenger runs, first flew in 1926. After two years' development, the prototype broke up in mid-air, killing the mechanic. The designer, Richard, fled to the Soviet Union, where he was involved in the development of the Tupolev ANT-20 bomber.
Having praised the lines of SPADs above, what can we make of the SPAD A.2? It was an attempt to combine the advantages of the pusher and tractor configurations. The observer was placed in a 'pulpit', forward of the propellor, from where he could not communicate with the pilot, and was in danger of being crushed from behind following even the mildest nose-over. Additionally, the observer himself, and the cage that had to be in place so that he did not shoot off his own propellor, so restricted the pilot's vision, he could hardly see to land. Nearly 100 were produced - unsurprisingly their crews hated them, and they were quickly withdrawn. The best you can say is that the work done on the general configuration paved the way for the successful S.7 and S.13.
There looks to be something missing from the Simplex-Arnoux Racer from 1922. The answer is probably 'stability'. It was an attempt to streamline by the virtual elimination of the tail, and used control surfaces that ran the whole width of the wing. The pilot sat behind the massive, drum-like radiator, so consequently could hardly see anything. The pilot was none other than wartime ace Georges Madon, who was lucky to escape with serious injuries.
The Potez 540 entered French service in 1934 as an escort fighter / reconnaissance / bomber type. Its armament was placed in manually operated turrets and hand-cranked ventral dustbin turrets. It saw action during the Spanish Civil War, where it was promptly nicknamed the Flying Coffin. The French immediately relegated them to transport duties.
The Amiot 143 was another type fulfilling the same role as the Potez (with a cruising speed of 168 kph!), but was converted to a bomber in pre-production. It was obsolete when war broke out, but the slowness of French aircraft production meant they had to carry on regardless. The aircraft of 34e and 38e Escadres took heavy losses trying to bomb the Meuse bridges from 800m in May 1940.
The Bloch MB.200 was cut from similar cloth as the Potez and Amiot, but was designed as a night bomber, and entered service in 1935. Over 200 were produced, and it was built under license in Czechoslovakia, but was obsolete almost as it entered service.
The Farman F.121 Jabiru may have been some kind of ancestor to all of them. The family of aircraft began with the F.60 Goliath, which began life as a bomber, but was converted for airline use after the end of the Great War. This spawned the F.120, 121, 122 and 123 - with the exception of the 121, all bombers in various configurations. The 121 illustrated is serving with Danish Air Lines.
And having found a style, the Farman company continued to follow it with the F.220 series, which included the 220 bomber (delivered to squadrons in 1936), the 221 bomber (with enclosed gunners' positions), the 222 (with retractable undercarriage), the twin-tailed 223 bomber or airliner, and the 224 airliner. With a maximum speed of 320kph (199mph) and a payload of 4,200kg, it was never going to set the world on fire, but aircraft of this type did raid Berlin twice, first on 7 June 1940 and again three days later.
An honourable mention for the Antoinette Monobloc of 1911, despite the imprimatur of pre-Great War aviation star Hubert Latham. The wheel spats give it a certain period charm, and the lack of bracing wires was ahead of his time, but it was actually too heavy to get off the ground, given the weak engines of the day.
On the grounds that their unusual configuration was because they were experimental machines, we could perhaps excuse the appearance of the Makhonine MAK.10 of 1931 (with telescopic wings!) Gerin Varivol of 1936 (more variable geometry), and the SNECMA C.450-01 Coléoptère of 1959 (an annular wing). Couldn't we?
Pictures: the photos come from the Virtual Aircraft Museum here, with the exception of those of the SPAD A.2 and Bloch MB.200, which are from Wikipedia.