If a person were congratulated begrudgingly or out of sympathy, is that a genuine pat on the back or something else?

If you congratulated someone on a promotion, a recognition, etc. and did not like the person, why would you do it? If it were at work or in class, would you feel obligated to do it because that is what is done, would you do so just out of GP, or sympathy? If you did not like the person why not pass on patting them in on the back, especially if they did not expect you to in the first place?