Pretentious

[Justin Bieber]

Definitely two meanings, and they really depend on the attitudes of the user, and what the user thinks is fake or real. So:
A) Pretentious can be a useful phrase to describe something that is fake or pretend, or somebody who is pretending in order to conform. Sometimes it is still used that way.
Its meaning has also become completely the opposite. In the English-speaking world, pretentious has become a catch-all phrase to criticize anything or anyone that is vaguely heartfelt, intellectual, earnest, sincere, artistic, unconventional, nonconformist, non-commercial, or not on TV, on Youtube or in the supermarket.

[Tanya Shivari]

To use [big words] to make yourself sound smarter than you actually are.

[Little_Girl]

displaying a self-image of being [special], intelligent, and different. not content with being average, and striving to be the best at everything and grabbing all attention. speaking in [cliches]. having no humility or originality.

[Mark Zuckerberg]

The most ironic word in the history of language.

[Rihanna]

Arent we all pretentious? Dont we all have some picture in our minds of ourselves that we aspire towards? Is that such a bad thing? Were all pretending, all the time. Idiots toss this word around not knowing what they really mean by it in my experience...they would probably say this definition is pretentious.

[Mark Zuckerberg]

A word that pretentious people use. If one uses the word pretentious then they are most likely trying to sound intelligent by using large words, therefore making them pretentious. (This results in a never-ending chain of pretentiousness.)

[Zipporah Schumaker]

To use [big words] to make yourself sound smarter than you actually are.

[Couch Potatoe]

Attempting to impress by affecting greater importance or merit than is actually possessed.

[Rihanna]

Behaving in an attention-seeking manner via presenting oneself on the surface as being intelligent, provocative, important, [avant-garde], humorous or significant, yet harboring [ulterior] motives, typically involving some form of personal gratification or [material gain] (e.g. advancement in social status, career, wealth, etc.).
Note that using this word is often conflated to be a pretentious act in and of itself, as this word is frequently used as a way to easily discredit people, works of art, ideas or statements while simultaneously boosting ones own status.

[Sommer]

The medical term for when someone manages to get their head so far [up their own ass], that you could [consider it] a [medical emergency].

Some call it serious but most people just call it annoying.

More common amongst teens usually emo or goth, but can still be spotted in adults. Best way to deal with these people is to just not give them the time of day.

[Magaret]

1. full of pretense or pretension.
2. characterized by assumption of dignity or importance.
3. making an exaggerated outward show; ostentatious.
4. any person who smokes a pipe while sitting in a big [leather chair] while wearing a fine sweater-vest in his study which is filled with [leather-bound books] and smells of [rich mahogany].