when a friend of mine looked up some other word on urban dictionary, she stumbled across 'mugly,' and was immediately able to figure out its etymology. (we guessed 'mother-fucking ugly,' but the site also lists 'mad ugly,' 'monkey-ugly' and 'man ugly.') at any rate, these formations all have something in common. they all take the onset (first consonant sound or group of consonant sounds) of the first word in a pair and use it to replace the onset of the second word. fans of the movie Mean Girls also encountered this in the word 'fugly,' and if you can guess what that means, then i feel justified in saying that this is a productive morphological process!
it's interesting that in most of these cases, the word-formation combines the first letters of an adverb with the end of an adjective to form a new adjective. also, the 'adverb' in some of the cases i cited above is just a noun placed before the word. this too is a pretty slang-ish usage, i think, and i read it as 'adjective as a noun,' like 'ugly as a monkey.' it also seems possible to derive a new noun by combining an adjective and noun in the same way.
some examples that i found on urban dictionary:
fonedit's amazing what we have words for. (though more than a few of these did not mean what i expected them to.) a couple use additional morphological processes (changing vowel sounds, inserting another consonant after the onset...) but seem to be based on the main one we're talking about here. also, note that many of them have alternate definitions; for instance, i'm not sure 'f' can be considered a true morpheme since it has multiple meanings ('fake,' 'fucking,' 'female').
fex (pretty much any consonant followed by -ex is a word, whether by this formation process or not)
mex (the first definition at least)
another key example is 'crunk,' a term made popular by rap producer lil jon (thank you urbandictionary). i always thought it was an adjective meaning 'crazy drunk,' since it has similar distribution distribution to 'drunk.' but, as evidenced by the contention on urban dictionary, the word has beaucoup de ambiguity. whereas 'drunk' (almost) exclusively applies to people, one can go to a 'crunk party,' and some claim there is a genre of music by the same name. there are also claims circulating that 'crunk' is a mix of 'chronic' and 'drunk,' and means to use alcohol and marijuana at the same time.
despite these ambiguities and alternate definitions, it's important to note that upon being introduced to a novel word a speaker of english slang can propose a systematic formation process. after hearing any one of these words we can create infinitely many more, whether we know the 'true meaning' or 'actual' formation process of the original example or not. after all, one example does not a pattern make. that is, it's possible that a morphological process actually becomes systematic for the first time when we try to come up with a coherent explanation for how morphology relates to meaning and then use the process (which the hearer has imagined!) to create more words. it's just possible.