Sometimes people deliberately deviate from the norms of speaking in a language. This is not due to their lack of communicative competence.
I would define the deliberate deviation from the norms of speaking as a communication strategy which aims to couch an additional message within the overt message by disregarding one of the four elements in communication described by Hymes (1972). In the example discussed below, the speaker disregards the rules for appropriateness in order to question an entire structure of social conventions he disapproves of.
On completing his work contract as a language teacher at a public school in Japan, a New Zealander friend of mine ended his farewell speech with
Osewa ni narimasen deshita (lit. ‘[I] was NOT taken good care of’ お世話になりませんでした)
I should add that the ‘appropriate’ phrase usually heard in this context is
Osewa ni narimashita (lit. ‘[I] was taken good care of’ お世話になりました)
commonly used to express gratitude after transacting business with somebody (especially when this involves receiving some services). In fact, Japanese communication typically relies on a large set of ‘fixed verbal formulas’ each of which is uniformly employed to achieve a communicative goal in a given context (Clancy 1986: 216-217).
My friend’s (grammatically correct) coinage probably stemmed from a general sense of dissatisfaction with the rigid structures prevailing in the Japanese public education system; by deliberately ignoring socio-cultural rules he tried to draw attention to the mismatch between form and reality (as he perceived it), even though he probably came across as ‘rude’ and even ‘aggressive’ (Cook 2003: 48).
Clancy, P. 1986, ‘The acquisition of communicative style in Japanese’, in Language Socialization Across Cultures, eds B. Shieffelin & E. Ochs, Cambridge University Press, Cambridge, pp. 213-250.
Cook, G. 2003, ‘Applied Linguistics’ (in the series Oxford Introduction to Language Study), Oxford University Press, Oxford.
Hymes, D.H. 1972, ‘On Communicative Competence’, in Sociolinguistics: Selected Readings, eds J. B. Pride & J. Holmes, Penguin, Harmondsworth, pp. 269-293