What would be your reaction?

I’d add the missing apostrophe and hand it back to him with a grim stare.

I’d look at the missing apostrophe and roll my eyes. Then I would giggle.

Hand them a note which reads “I like your mom when you’re not there.”

I don’t live in a house, so I wouldn’t care much. I’d just throw it away.

Hand them a note which reads: “Your what?”

Jokes on you! I don’t own a house!

I’d offer the note back to wipe the blood from their nose.

The missing apostrophe has been handled already by others. I would ask Pat for a vowel to follow the “R”; probably “E”.
Since nothing is missing, or out of place, I would have to assume this person is either lieing, or a very neat, respectful visitor, or they like to hang around outside of empty houses. I guess I would say thank you, and that I feel the same. I like my house when they are not there.

Ha! I would say, hey! When you are there, how about doing some dishes!

I’d check the back of their ankles. No nip marks, they’re lying. My dog is quite the nipper.

I’m ALWAYS there so you won’t be liking it much anymore.

I’d immediately check his grammar.

Smile politely and then invite them over immediately…

Correctly spelled – “you’re” to replace “you are”

I’d raise an eyebrow and scoff. Nobody likes my house when we’re not there- our two large, extremely loud dogs wouldn’t be very happy with a stranger in the house.

I’d ask him how he managed to escape when my German Shepherd went for his jugular.

Report them as a stalker. A threatening stalker at that.
Hand the note to the Police.

A stalker with bad grammar. Let’s not forget the grammar.

I’d politely ask them what they meant by that & probably make a citizens arrest. I don’t take threats lightly.