Can something be "extremely mediocre"?

This doesn't sound quite right to me, but I can't explain why. I can understand an extreme sense of mediocrity one can get from something but does that justify the usage of "extreme" with "mediocre"?

Something can be 'very mediocre', 'completely mediocre', etc.

If it's 'extremely mediocre' though, you're crossing the line into parody. It can be used as a humorous hyperbole, the same as "fantastically bland" or "Totally averagest of them all". It makes for a very poor expression in serious contexts though.

If you approach it purely semantically, mediocre, middle-of-the-road, average, normal, etc. seem to be absolutes that can not have comparatives or superlatives.

The same happens with absolute superlatives like perfect.

It is semantically wrong to state (although admittedly most speakers have no problem with it at all):

Solution A is more perfect than solution B.

( http://en.wiktionary.org/wiki/perfect Its meaning is "done", "finished" originally, and as in "practice makes perfect", it indicates that it as the absolute done versus not done. Also grammatically, a perfect tense indicates something that is finished, not something that is in some state of getting finished eventually)

However, if you want to indicate that something really has nothing to distinguish it from the average, that it is actually nearly invisible, you can express that by qualifying how average it is: "his appearance was so average as to become almost invisible".

By doing this, you do actually modify the "neutral" average in a negative way (that is, I have never seen it with positive connotations.)

Mediocre, although as such neutral, already has negative connotations. You can reinforce those connotations by indicating that the mediocrity in this case actually has a stronger effect than you would normally expect of mediocrity by using extremely mediocre.

Another example might be neutrality. If a country is neutral in a conflict, that is normally an absolute, you are neutral or you are not. One could however, comment on Swiss's historical neutrality by calling them "extremely neutral".

In the same way, normally one is either pregnant or not, This is also an absolute. I have heard people describe a woman in her last weeks as being "extremely pregnant" though.

So, even though we can normally not compare absolutes like perfect, mediocre, average, pregnant or neutral, it is acceptable_ to do so in order to convey a related, but more detailed meaning of the absolute. Always be aware that the meaning will usually change:

Extremely average (so average as to become negative).

Extremely pregnant (the pregnancy won't last much longer).

Extremely neutral (probably indicates the speaker does not regard it as real neutrality anymore).

EnglishClub has a good article on gradable and non-gradable adjectives, containing:

Some qualities can vary in intensity or grade (for example: rather hot, hot, very hot; hot, hotter, the hottest).

The adjective hot is gradable.

Other qualities cannot vary in intensity or grade because they are:

extremes (for example: freezing)

absolutes (for example: dead); – or

classifying (for example: nuclear)

('Almost' etc may be used with the first two categories; freezing point can be approached on a temperature scale, but the approach to death is harder to measure accurately!)

I wouldn't include 'mediocre' in the 'extreme' category! One could easily argue that it can't sensibly be graded. However, usage often doesn't follow logic. 'Extremely mediocre' sounds a crazy juxtaposition, as SF says; 'very mediocre' doesn't sound as wacky but would probably be used to mean 'way below average' rather than 'very close to the mean'.

Even with obviously extreme adjectives, illogical-looking grading is sometimes used to save words:

This bucket is very full (meaning This bucket is very nearly full).

'[M]ore perfect' in the US constitution is a similar ellipsis from 'more nearly perfect'.

I've had wine that was extremely mediocre. About the only thing you could note on its tasting notes was "tastes a bit like wine". There was a water-like quality to most of the palate, though not with the weakness that watery would imply.

There was nothing bad about it; no throat-scratching tannins, or bitterness. There was nothing unpleasant to the after-taste, because it didn't have the length to have any after-taste at all.

Indeed, it would almost have been better if there was something bad about it, because then at least there'd have been something of interest in the bottle.

In all, it was remarkable just how extremely mediocre it was. My father-in-law and I drank our way through quite a bit of it struggling to find something to say about it before we saw sense and opened something worth drinking.

So yeah, something can be extremely mediocre, (and quite expensive too, not that that's relevant).

The problem is, I don't think I'd have managed to convey that this wine was extremely mediocre just by calling it "extremely mediocre"; that we can find a way in which a phrase is valid doesn't necessarily make it good or useful.