;You are being 'ideological'' - but what dos ideology actually mean?

The term ideology designates a system of representations that offer the subject an imaginary, compelling, sense of reality in which crucial contradictions of self and social order appear resolved. 

Good that done lets investigate ideology further:

Ideology is less a set of explicit political ideas than a set of pre-conscious image-concepts in which men and women see and experience, before they think about, their place within a a given social formation, with its specific structure of class and gender relations.

 Ideology is imaginary not because it is in any sense unreal, but because it gives the subject an image that satisfies an unconscious need for coherence, an image that is in fact the specular (pertaining to or having the properties of a mirror) means for constructing the subject

 Contemporary Marxism understands that the subtlest and strongest forms of ideological address are those pitched not in narrowly political or abstractly conceptual terms, but those --including what we call literature and art-- pitched in concrete, overdetermined images appealing to the primary unconscious fears and desires that underpin the subject's sense of reality and identity. It is this "reality-effect" --the capacity of certain discursive and dramatic practices to disturb or displace prevailing forms of social and sexual subject-ion through an address to the unconscious-- that has prompted recurring demands for the exclusion, and schemes for the management, of such practices.

Of course, ideology is always politically significant, because the lived relation to the real in which it situates the subject provides the condition of political thought and practical activity, and solicits the subject's free (even if grudging) participation in a social world experienced as natural and inevitable. 

Ideologies address, fascinate, worry, and fix social subjects in ways appropriate to the reproduction of a given social order; they present as obvious, simple, and universal --as reality itself-- what is peculiar, complex, and historically specific. Ideological work is always directly or indirectly affiliated with political work, constructing a realm of experience that seems to universalize and stabilize a social project serving particular class interests."
"Ideology" is also a  complex of distinctive practices and social relations which are characteristic of any society and which are inscribed in the language of that society. 

"Ideology" therefore applies to all the largely unconscious assumptions and acts by which men and women relate to their world; it is the system of images, attitudes, feelings, myths, and gestures which are peculiar to a society, which the members who make up that society habitually take for granted.

All societies are held together by ideology. In any society, one of the functions of ideology is, as far as possible, to define and limit the linguistic and cultural practices by which members of that society function. If, as usually happens, a society likes to think of itself as harmonious, coherent, and consensual, then it is ideology that enables this to occur. It tries to suggest the existing order of things is permanent, natural, universally acknowledged, embodying truths we would all agree with -- and in so far as it persuades us that such "truths" are not ideology. Ideology helps bind us together by giving us seemingly coherent representations and explanations of our social practices, and in particular by giving us the language by which we describe and thus try to perpetuate them. Thus ideology acts as a kind of social glue, binding us all together.

References: ((Althusser 1970, pp. 231ff Althusser 1971, pp. 162ff; Belsey 1980, pp. 55-6 (Machery and Balibar 1980, p. 53) ary Waller, English Poetry of the Sixteenth Century, p. 9:).