Do not ever approach the pharmacy counter at Watson's thinking it's a cashier counter. The pharmacist there takes a dim view of your mistake and will curtly tell you that the cashier counter is behind you.
Then when you politely tell her it was rather rude of her, she will say she thought from your appearance, that you are an intelligent person and can read the giant sign hanging high above her esteemed counter that said "Pharmacy".
In other words, she is implying you were blind and stupid for not being able to tell that her holy pharmacy counter is not the cashier's.
According to her, people mistaking her pharmacy counter as the cashier's happens a lot. But she tells you it's the first time anyone told her she was rude.
It's a pity. The cashiers at the actual cashier's counter were extremely polite and professional, and even apologised when I told them their pharmacist was rude.
I told them it was not their fault, and that their service was exemplary. Watson's just needs to train their pharmacists to be as polite as their counter staff.
When I used to work in retail, people always mistook the info counter for the cashier counter. But we were all trained to tell customers nicely, with a smile, where the actual cashier's counter was. And never to make a customer feel stupid for making the mistake or to use sarcasm when the customer complained of poor service.
I suggest you try it and see. Go to Watson's Tampines Mall and mistake the Pharmacy counter for the cashier's. Maybe I'm the only one who got dissed. Or maybe you'll get the same treatment. If you get the same curt treatment, let her know. So I won't be the only person to tell her so.