(I'm easily irritated, it appears)
My former flatmates were forever accusing me of being "too fussy" about language. Every time I made a comment or corrected their grammar, they would call me the "grammar police"
Now, I don't object to them disliking my habit of correcting people's speech (I'm aware it can be annoying) but it bothers me a little that (apparently) I have taken on the status of an entire disciplinary force!
Either "grammar policewoman", "grammar police officer" would work but "grammar police"? Police is a collective noun, which implies I have a lot more personalities than the six I actually have...
This is a good example, I feel, of at least one of the reasons some of these linguistic changes occur: it's far quicker and catchier to say (in this case) "police", than "policewoman" or "police officer".
Basically, we're a lazy race!
I've become even more aware of my own linguistic shortcomings recently, through constant contact with speakers of other languages.
It's a bit embarrassing to have to repeat yourself, when speaking to a non-native speaker of your language, when you realize the need for repetition has been caused by your own lazy pronunciation, not their inability to understand you!