Is it appropriate to discuss the weather at work?
Yes!
The weather is an appropriate workplace conversation.

No
It is important to wear clean clothing to work.
Is it appropriate to discuss farting or pooping at work?
No!
This is not an appropriate topic for the workplace or polite conversation.

Yes
If your job has a uniform, you should always wear that to work.
Is it appropriate to discuss weekend or vacation plans at work?
Yes!
Weekend and vacation plans are an appropriate workplace conversation.
Is it appropriate to discuss sports at work?
Yes.
Just be aware that your coworkers may not support the same teams you do
Is it appropriate to discuss religion or politics at work?
Sometimes.
While these topics are not inappropriate, be aware that some of your coworkers may have different beliefs and could be uncomfortable with your views.