"Fuck"
Really, people. This is supposed to be a highly offensive word used in times of great duress or frustration. Lacing it into every sentence just reduces the impact of the word down to almost nothing. You're not being edgy or creative anymore, and it's just boring.
Oh sure, cluster F-bombs can be extremely effective (not to mention hilarious) if done right. But all too often, I hear sentences like this: "I don't fucking know, just fucking move that fucking box the fuck over there." Really, this is a mundane order, and the use of an explicative (not to mention several of them) is completely unnecessary. It reaches the point that when the word should reinforce the nature and severity of a sentence (i.e. "You fucking asshole"), it ends up serving no other purpose than just being a filler.
In summary: I wish people would learn to cuss creatively.