You know what really grinds my gears?
When I'm signing up for a service that requires an email account and they don't know how to properly validate email addresses. The + is valid in an email address.
It's not only legit, it's really useful.
What do you do about it?
I use the dots if it's something I really need to sign up for. Also, any message I get from a website that doesn't have the firstname.lastname@example.org I mark as spam.