Sure. One time, a sign in a store said 'Apple's for sale'. It should be 'Apples are for sale'. Another was a student who wrote 'I goed to the park'. Hilarious!
One bad grammar horror story could be a sign that says 'Let's eat, grandma!' instead of 'Let's eat grandma!'. The wrong punctuation completely changes the meaning. It could be really horrifying if someone actually thought the latter was the intention.
The most common one is probably the confusion between 'there', 'their' and 'they're'. People often write things like 'There going to the park' when it should be 'They're going to the park'. It's a simple mistake but can make the text seem unprofessional.
Probably the confusion between 'its' and 'it's'. Many write 'The dog chased it's tail' when it should be 'The dog chased its tail'. Also, the incorrect use of verb tenses, such as 'I runned to the store' instead of 'I ran to the store' are some of the most common and funny grammar stories.
The unexpectedness. We're used to proper grammar, so when we encounter bad grammar in a spooky context, it jars our senses. It's like something is off in the very fabric of the communication, which adds to the fear factor.
Once upon a time, there was a sign that said 'No enter'. A man ignored it and entered. Strange things started to happen. The room seemed to shift and voices whispered with wrong grammar like 'You no should be here'. He soon realized that the bad grammar was part of the curse in this place.
Sure. There was a student who wrote 'I have a good news'. The correct form should be 'I have good news' as 'news' is uncountable. Another one is when someone said 'Me and my friend went to the park'. It should be 'My friend and I went to the park' for proper subject form.
Well, in 'Harry Potter Bad Grammar Fanfiction', you might find sentences that lack proper punctuation. Like a long run - on sentence 'Harry was walking in the forest he saw a strange creature it looked very scary' without any commas or periods. And then there are cases of wrong word order, perhaps something like 'To Hogwarts Harry went' which is an archaic or just incorrect way of stating 'Harry went to Hogwarts'.