In the beginning (as far back as the '80s), there was weak sauce. Laid back California dudes and college jocks alike wielded it in judgment of the uninspiring. Weak sauce at first hovered between noun phrase and adjective. It could literally refer to a type of sauce (that was lacking in flavor or alcoholic content), but as a whole it meant “lame.” Eventually it became a single concept (reflected in the spellings weaksauce or weak-sauce) and an unambiguous adjective—you could say things like “that is so weaksauce” rather than “that is such weak sauce.”
What then, was the opposite of weaksauce? Cool, rad, and awesome did the trick for a while, but in the early 2000s, analogy kicked in to produce awesomesauce. Awesomesauce not only had the casual, slangy vibe of weaksauce, it had a melodious sound profile. There was the similarity of the “awe” and “sauce” vowels, the repeated s-sounds.
Once sauce had wandered over to another word, there was nothing to stop it from continuing to mix it up all over the place, becoming a new kind of suffix. The following decade brought us lamesauce, crazysauce, wacksauce, dopesauce, and awkward-sauce. After a point, -sauce didn’t even need to attach to an adjective anymore. Scattered through the internet are the likes of failsauce, winsauce, nerdsauce, pwnsauce and WTFsauce. In fact, the more “memey” the expression, the better it seems to fit. According to the implicit rules of “sauce” affixation, carpe diem sauce sounds weird, but YOLOsauce sounds about right.
Sauce has come a long way from its original noun meaning, passing through idiom, to adjective, to adjective-forming suffix. Still, it has kept in touch with its roots. A party can be described simply as awesomesauce, but it can also be “covered in awesomesauce.” A movie can be lamesauce, but it can also be “marinated in lamesauce.” The saucy aspects of the -sauce suffix can be reactivated at will by the creative user. Just another example of the way we humans like to add a little flavor to our language.