One thing that bothers me to no end is when I see sites or apps using the wrong form of "Log in." I used to have a little poster for this and I decided to bring it to the masses with another classic 2 minute read for Medium. Go read the article and pass it on. I specifically call out companies that make this mistake and I want them to hear about it.
Pro tip: use Sign In instead and then you never have to worry about making this mistake.