I hate it when people leave words out of sentences. For example, when someone says "all the sudden" instead of "all of the sudden". Granted, I think using suddenly is more efficient in that case, but no matter.
I also hate it when people leave "to be" out of their usual speech. For example, I had to talk to a customer at my shop about his Dodge Caravan. It's making a clunking sound in the front end when going over bumps, which I diagnosed as being bad strut mounts. The conversation went like this:
Me: The clunking noise in the front end of your van is the strut mounts making noise. It's a common fail point on these vans. I also recommend that you replace the struts at the same time, since I have to take them off of the van and disassemble them anyway. (calm voice)
Him: How do you know that the strut mount need replaced? (calm voice)
Me: The mounts are making noise. I've seen it a million times in the 10 years I've been repairing cars. (calm voice)
Him: I don't think that they need replaced. I think you're just trying to take my money. (yelling at the top of his lungs)
Me: Well, if that's the way you feel I'll be more than happy to put the wheels back on your van and put it back outside and you can live with the noise. Makes no difference to me. My car's not going to make clunking noises on the way home. (calm voice, scowl)
Him: You're very rude. You shouldn't treat customers like that. (yelling)
Me: I'm not paid to talk to customers at all. I'm paid to turn a wrench. You asked me what was wrong with your van, I told you and you didn't like my answer. Now, I'm going to go back into the shop and get back to work. (low, angry voice)