For example...
"Hence the reason for..."
Okay, it's just hence. "Hence" means "this is the reason for". So, by saying that, one is saying "This is the reason for the reason for...".
Then there's people who have no clue what they're talking about. A guy in one of my classes once said (about writing lengthy code):
"I hate doing this motononous work."
Wow, way to butcher a good word...

You know what's even more annoying? When people think that someone has a really high intelligence just because they use these "big words".
Here's a direct quote from a girl in my psych class about Mr "Motononous" up there...
"You're really smart. Like, you use all those big words all the time."
FUCK! He's a moron! He just impresses people with "big" words. Go pick up a frigging dictionary, moron!
Even worse, this same guy (again) impresses teachers by using the thesaurus in Word, so that his papers sound more professional. I've seen him do it.
People really need to learn the english language.
Now, I'm not saying that I'm perfect in any way. Far from it, in fact. But people really need to make more of an effort...
[/rant]