Answer: spelling.
Other findings:
– 59% of people get peeved when they see spelling mistakes on restaurant menus, store signs and ads
– 71% of people often find spelling mistakes when looking at writing from others
– 59% of people say improper grammar is their biggest beef when it comes to the English language
– 38% of people have a hard time spelling “February”
– 31% of people have a hard time spelling “definitely”
– 46% of people are confused when having to spell and use “their, they’re and there.”