Given the discussions on the language used in subtitles that crop up from time to time, I was wondering how familiar those who comment are with English grammar. Most of these are relatively easy constructions, so even a perfect score doesn't guarantee that you're an expert on grammar

You get one point if you correctly determine whether or not the sentence is grammatical. You get an additional point if the sentence is ungrammatical and you correctly identify the problem. Note that the sentences are intended to stand on their own and should be evaluated as such.
His singing in the shower vexes me.
I'm visiting mom and dad over the weekend.
Ungrammatical—capitalize mom and dad.
No one is above using their power for personal gain.
Ungrammatical—no one is singular whereas their is plural.
Were it up to me, I'd do it myself.
Me having been to Japan made it easier for me to understand her.
Ungrammatical—should be possessive + gerund, i.e., "My having been to Japan" rather than "Me having been to Japan."
You need to be careful John.
Ungrammatical—direct address, so it should be "You need to be careful, John."
Jenny and I are going to the theatre.
Who do you love?
Ungrammatical—use the objective case, i.e., "Whom do you love?"
Having finished the job, we returned home.
There's a lot of Finns in Sweden.
Ungrammatical—compare there are.
There are less calories in this, though.
Ungrammatical—fewer calories.
He's performed well in the past, however I don't think it'll be enough tonight.
Ungrammatical—however cannot be used to join two independent clauses. A possible solution would be "He's performed well in the past; however, I don't think it'll be enough tonight."
I bought a beautiful Japanese small vase.
Ungrammatical—incorrect order of adjectives. Compare "I bought a beautiful small Japanese vase."
The house is different from how I remember it.
We took shelter from the storm in a small cabin, and were pleasantly surprised to find it rather comfortable.
Ungrammatical—don't separate a verb phrase from its subject. Remove the comma or reword the sentence using a participal phrase, e.g., "Taking shelter from the storm in a small cabin, we were pleasantly surprised to find it rather comfortable."
Five grammatical and ten ungrammatical sentences, for a total of twenty-five points.
P.S. I scanned through this quickly, but if there are any problems, feel free to point them out
