The Curtiss-Wright XP-55 Ascender (pejoritavely nicknamed the Ass-Ender) was so laden with quick fixes to its aerodynamic quirks that it looked terribly offensive to me:
https://en.wikipedia.org/wiki/Curtiss-Wright_XP-55_Ascender
It was a precursor to engine-in-fuselage jet aircraft design, but it sure was not a ''clean'' aircraft. The Vultee XP-54 and Northrop XP-56 prototypes of the same era (referenced in the Wikipedia article) are equally bizarre-looking.