How is my grammar and punctuation in the folowing paragraph?

Picture this, you are taking a test and the person next to you is chewing their gum loudly,so you can't concentrate. How disrespectful is that? The school board needs to make a rule no chewing gum in school.

The first "sentence" is a run on.

The third sentence needs additional punctuation or words.

Picture this. You are taking a test and the person next to you is chewing their gum loudly. You can't concentrate. How disrepectful is that? The school board should have rules for no gum at school.

That is much better! :-)

To evaluate the grammar and punctuation in the given paragraph, we need to go through it step by step.

"Picture this, you are taking a test and the person next to you is chewing their gum loudly, so you can't concentrate."

- The first sentence begins with a capital letter, which indicates correct sentence structure.
- "Picture this" is an idiomatic expression, so it doesn't follow standard grammar rules. It is fine in this context.

"How disrespectful is that? The school board needs to make a rule no chewing gum in school."

- The second sentence is a question, and it ends with a question mark. This is appropriate punctuation.
- The phrase "The school board needs to make a rule" is a statement and should end with a period instead of a question mark.
- "No chewing gum in school" should be "against chewing gum in school" or "prohibiting chewing gum in school" to make the sentence grammatically correct.

Revised paragraph:

"Picture this: You are taking a test, and the person next to you is chewing their gum loudly, so you can't concentrate. How disrespectful is that? The school board needs to make a rule against chewing gum in school."

Please note that grammar and punctuation rules may vary depending on the style guide you are following.