It really bothers me because it's petty and annoying. Discreetly is one thing ... under the table but I have seen people make a "big show" of it more than once. I feel like the OP is referring to people who make it obvious to the waiter that they are calculating to the penny.

It is poor manners.

Poor manners bother me.

People who use excuses as to why they are "unable" to adhere to decent manners thus skirt any personal responsibility annoy me.