Edumacate yoselves 

Especially with all the native English speakers on here!

The truly irredeemable mistakes are the confusion of its/it's and they're/there/their. These confusions happen so often that they're not even worth calling out most of the time, but they are such unbelievably simple distinctions.

The second tier of somewhat more forgivable mistakes consists of confusing homonyms and words that have similar meanings, like saying "it effects me" (effect is a noun) instead of "it affects me" (affect is a verb) or "I like to lay on the couch" (lay is something you do to something else) instead of "I like to lie on the couch" (you are the one doing the action).

Similar to this is misusing common phrases, such as "used to." There is no instance in which you would use "use to." Another example of this is saying "I could care less" instead of "I could not care less."

The last tier is incorrectly using common idioms. One phrase I personally hate the misuse of is "I cried all the way to the bank." Many times, I will see it incorrectly written as "I laughed all the way to the bank." This phrase is credited to Liberace, a flamboyant and somewhat tacky piano player that was idolized by housewives. He coined this term when he received heavy criticism from acclaimed music critics. He "cried" all the way to the bank because though he wasn't regarded as an extraordinary musician in the eyes of these critics, he still made a ton of money. Replacing the crying with laughter takes some of the cynicism out of the phrase. A common idiom that takes less context to understand correct usage of is "shoo-in," which is frequently and incorrectly written as "shoe-in."