People who can't be bothered (or don't know) proper english punctuation and can't be bothered to learn.
It's and its
there, their and they're
using apostrophes on plurals "I am going to have bagel's"
Using txt speak ("r u going 2nite?") in online forums and other places where there is no limit on number of characters in a message.
"Listen, or your tongue will make you deaf." - Native American Proverb