Just because a credit card declines does not mean the person is a broke, on the verge of bankruptcy and a low class dumbass.
Credit cards get declined for various reasons and many times have nothing to do with the actual cardholder. Sometimes when a credit card declines it's actually a good thing. The person in front of you may not be the actual cardholder.
We have this new process on our VISA cards where if you buy something that is outside of your normal shopping pattern or use your card at stores where there is high fraud issues or that you haven't shopped at before, the card will decline so the cardholder will call us and we can verify that it is infact them attempting the purchase. Then they want to go all Sally-snap-out because of how humiliated they were. GET OVER IT! You'd be way more pissed calling in when you received your next statement and see a $3k charge that you didn't make, no?
Seriously, a credit card declining is not the end of the world nor is it always a bad thing.
Another example. Just because you made your credit card payment doesn't mean we received it. You may not have sent it out when you thought, the mail could have gotten lost en route or maybe we applied it to the wrong account. Regardless, if your card didn't decline when you tried using it, then you wouldn't have found out it was past due until you received your next statement (assuming you do-see before examples!) which could very well be 30+ days later. Holy credit bureau Batman! You'd be much more unhappy than if you got a copy of your credit report and had a negative mark and then had to go through the FCRA dispute process that takes F-O-R-E-V-E-R.
So please remember that it's not embarassing when a credit card declines and make no judgements about the person and his/her card that just declined in line before you.