Plz use English correctly b4 i cry k thx

Language is a pretty important thing. We couldn't hope to communicate with each other effectively enough to maintain our society's infrastructure without it. So it's rather nice if people deign to use it correctly.
For instance, this gets to me: If I select a bottle of wine for £2.99, take it to the counter to pay for it and am told, "That'll be two ninety-nine, please," I should by all rights be confused. I am always tempted to reply, "It will be 2.99? Well, what price is it now?" (Of course, I would then have the enriching experience of seeing the yout' behind the counter regard me like he would a space crustacean for a second before going, "Uhhhh ... ummmmm ... hold on, let me get the manager.") Some cashiers do get it right the first time and announce, "That's 2.99, please." But it's the "gonna be" and "will be" that irks me. At what point in the history of English did people decide that using the future tense to refer to the immediate present was acceptable?
But the misuse or total exclusion of apostrophes is what really gets my dander up. I experience a brief but intense flash of temper everytime I see one out of place or dropped altogther. For instance, in our kitchen area at work, there's a sign above the counter imploring us to "please rinse out your bowl's/plate's before putting them into the sink." I used to think that this was commonplace in America due to our dumbed-down liberal education system, but the disease has taken place here too. And then you have corporations like Tesco, a dominant supermarket chain, who announce their line of clothing as "Mens," "Womens" or "Childrens." The writer Bill Bryson excoriated them for this and I am pretty disgusted and alarmed by it as well.
Honestly, is it so hard to use an apostrophe correctly? Is it that taxing on the brain to know when to use "its" versus "it's" or "your" versus "you're"? In fact, I'm beginning to think an ever-increasing number of folks are completely unaware of the form "you're."
Then there's "could/would/should of." I wish people would stop to analyze this. Does "could of" make any orthographical sense? Does it make any sense at all? The problem, of course, is that the past tense "have" is often shortened to -'ve, which sounds exactly like "of." But they are two completely different syllables.
Don't even get me started on this curse known as texting. I could write 100 pages in a state of high piss-off about how much I deplore it and the effect it's having on people's ability to speak, write and spell properly.
Now defending the proper use of English can go too far. The British anchorman John Humphrys gives a classic example in his book "Beyond Words." He writes of people who scoff when offered a nice cup of tea. "What these people want," Humphrys says, "is a cup of nice tea." Even though, he continues, it doesn't take any effort for an English speaker to deduce that it's the tea, not the cup, being referred to as nice, some people are adamant about the correct word order. This could be seen as extremism. After all, the cup of tea is regarded as a collective whole; it's the cup containing the tea that makes it nice. Indeed, if you really wanted to be a schtickler for the correct use of language, you could say that "nice cup of tea" makes no sense at all. Cups of tea aren't charitable nor do they pat us on the back and tell us what a wonderful person we are. A good cup of tea is what we should offer people. However, "nice cup of tea" just became such common parlance in the language that it became accepted to the point where no-one thinks about it.
Which brings me back to my original point. How long can it be before society enshrines "your" to mean you are, "it's" as the possessive form of it, and "could of" to denote could have, because no-one, not even people in positions of power, knows any better? How long, indeed, before we drop the apostrophe, such a useful tool?
Now, dear reader, you may understand why I get annoyed at being told that my bottle of wine "will be" £2.99. That casual misuse of tense just reminds me of the inexorable slide toward a form of English that I no longer recognize, one that will make me weep because I love the language too much to see the scars of its abuse become official.