1. Incorrect use of the word 'impact' especially as a verb.
2. Missing out the object of a transitive verb, as if the reader or listener won't miss it.
3. Switching from singular to plural half way through a sentence, especially the use of the word 'they' instead of 'he'.
4. Not being able to distinguish between a verb, a noun and a gerund, especially when using reflexive verb. There is no verb in the English language that begins with 'self'.
5. Referring to married women by their husbands' surnames. Noboby would treat a man like that. If you don't know what a married woman's surname is then it is correct to refer to her by her husband's name in full, e.g. Mrs. John Smith. If she doesn't like it, tough!