One sentence or less
I personally believe every topic should be explainable in one sentence or less.  For example,
Mechanical Engineering - The study and application of position, velocity, and acceleration to determine the forces and moments acting on an object.

Christianity - The religion that emphasizes personal salvation through the sacrifice of Jesus Christ as a means of accessing and drawing closer to the God of heaven and earth.

Rocket Science - The study of objects in flight assisted by an active propelling force.
See?  Simple.  Whenever I need to ask a long talker to explain something, I usually specify to do it in one sentence or less.  If they can't, they're not trying hard enough.  If they don't, I don't listen. #language

Permit and insurance (2)
Two words often mispronounced (according to Dave's Most Excellent and Perfect Guide to English Pronunciation™): 
  1. Permit.  A year before you get your driver's license, you get your learner's permit, as in permit, not permit.  You can permit something (used as a verb), while a permit allows you to do something (used as a noun).
  2. Insurance.  In order to drive a car, you need to have car insurance, as in insurance, not insurance.  This is largely a southern problem.
Please comply. #language

Authorized personnel
I see a lot of signs at work and in public places that say something like "This area is off limits to unauthorized personnel".  This is an examples of a rhetorical tautology, i.e. "an unnecessary (and usually unintentional) repetition of meaning, using different words that effectively say the same thing twice".  The area is off limits because the personnel aren't authorized to be there.  The personnel aren't authorized to be there because it's off limits to them.  And so on. #language

Somewheres
I sit near a guy at work who's a friggin genius.  He's literally incredibly smart and could literally be considered a rocket scientist because of the nature of his work. 

But he has one very major flaw:  He uses the word "somewheres" instead of the correct word "somewhere". 

Linguists politely say "somewheres" is a nonstandard or "common" form of the word.  I say it's wrong.  It's completely and utterly wrong, and yes, it makes you sound dumb. 

The thing is, I hardly know anyone who uses this word.  There was my 3rd and 4th grade little league coach, but that was the least of his problems.  My 4th grade football coach might've also used the word (uh oh ... am I seeing a parallel between sports and stupidity?), but again, that wasn't his greatest fault.  Intelligent and uneducated people alike generally don't use the word "somewheres". 

The other thing is that this smart guy uses this word probably 60 to 70 times a day.  "That paper is around here somewheres."  "You take a right somewheres around the bend in the road."  "My son goes to school somewheres near New York."  If I counted the number of times I say the word "somewhere", it would be around 4 or 5 times a week.  Maybe.  This guy not only says the wrong word, he says it a lot.  It's irritating to say the least, especially for a nerd like me. #language

Heighth
Even though "heighth" is technically an acceptable variation of the word "height", and even though it actually makes more sense than "height" because it matches the other words corresponding to measurement (length, width, depth), I still don't like it.  I think it makes the user sound less intelligent.  Sorry, heighth users. #language

Multitasking is dumb
Multitasking:  Working on several things at once, completing none of them. #language

No accent (6)
I'm fully convinced I have no accent.  I'm sure that's how everyone feels about their own brand of English, but they're all wrong.  I can hear the slightest accent in a person's voice, and I absolutely feel like my version of English is completely free of any of these accents.  I grew up in northern New Jersey, but I definitely don't have a New York accent.  My parents were from south Jersey, but I don't have a Philly accent.  I'm obviously not southern, nor am I midwestern, each of which have their own specific and separate accents.  I'm completely accent free.  Someone please prove me wrong. #language

Pun intended (1)
Why are people so opposed to using puns?  The phrase "no pun intended" has become so ingrained in our language that we parenthetically include it in our speech without a second thought.  I think we should embrace puns and all their stupid funniness.  Use puns intentionally. 

On a side note, why do so many people know that the definition of a pun is "a play on words"?  Were we all force-fed the same vocabulary textbook in 7th grade? #language

Different English accents
I can't tell the difference between Irish, Scottish, British, and Australian accents.  They all sound the same to me even though I know they're different.  If I hear one right next to another, I can usually tell the difference.  But I've found that I'm heavily influenced by context.  A British person in Australia will sound Australian to me.  An Irish person in South Africa will sound British.  All I know is that they're not American. #language

Shortened forms of short words (6)
My sister likes to use "ck" as a shortened form of the word "check", as in, "I'll ck on that as soon as I can."  It's annoying.  Please stop. 

For one, the word "check" is already short enough.  It's five letters long.  Did we really need to invent a word to shorten a five-letter word?  I don't think so. 

Second of all, you're the only person in the universe who uses this shortened form.  It's not common among the general population like "IRS" or "CNN".  It's not even common with the young kids with their "lol" and their "cya".  Nobody knows what "ck" means.  Every time we read it in one of your emails, we have to stop and analyze the context clues in the sentence to determine the word's meaning. 

Third, it's the only word you chose to shorten.  It's not like you made up this whole shortened language where every word longer than four letters has a shortened form.  Nope.  You write everything normal, and then spring a "ck" out of nowhere.  This is unacceptable.  Please stop. #language