I think one of the most common grammar mistakes is saying aint instead of are not or aren’t. Another thing is that adverb clauses are not independent clauses, so they cannot stand alone as sentences. Some examples of this are:
After it rains-It rains.
Although she was biking-She was biking.
While the cell’s shape changed-The cell’s shape kept [...]

Comment here with one or two examples of poor grammar.
They can be from anywhere or anyone (you may want to hide or obscure identifying information to protect the grammatically ignorant).
Be sure to give an explanation about what is wrong with it (so we know you know, and to teach those who may not yet know).
A [...]

We’ve been talking a lot about grammar over the past several classes. We’ve mostly focused on how to do it correctly, and why. But the bad examples are feeling left out, so it is up to you to share some with us.
So, post a comment here and share an example of poor grammar (keep the [...]