If you have a very serious problem with your work superiors, would it affect your mood with the customer?

Yes, it does just cool and pay heed on your job.

That shouldn't happen, because customer doesn't deserve your grin.
But in reality, that happens a lot.

You should not have a problem with your superior in the first place, if you do it means there is something wrong that needs to be fixed from its roots.
You should not let your relationship with your superior affect the way you feel about your job or the way you serve your customers.
Try to calm your self and think about a solution for your problem, usually being assertive and talking to him will fix any miss understanding.

yes, but still you should have focus your job obligations.

No.
you should focus on how to serve your customers.