No. There are hair products that that use the word "mayonnaise" in them but it is not the mayonnaise you eat.
You don't usually need mayonnaise to make pancakes.
If you mean 'Why doesn't the oil separate in the mayonnaise?', then that would be due to the egg yolks added to it. Egg yolks are known for their binding qualities amongst other things.
You can't. Your hair will grow or not grow with or without mayonnaise.
They don't make cheese with mayonnaise
Yes, they do.
To make a pickle-mayonnaise topping, chop a pickle into small pieces and mix it in mayonnaise in a bowl before spreading it on a sandwich.
Sitting down
Yes, no problem. Making or cooking, doing something doesn't stop because you have a period. This is a natural body function that you will have for a good 50 years and there is no reason why you can't do everything you normally do.
probably not
the yolk
no not at all fruits and vegetables do