Restaurant charged me an extra $20 on my credit card bill when I already gave $20 in cash for tips ?

If you don't want the tip on your credit card, you would have put $0.00 on the tip line and moved down $181.10 to the total line.

What you did is tipped $20 on your credit card AND tipped $20 in cash. But it's all good because $20 is a crappy tip for a $181.10 bill.

20% would have been $36.

You are naive. When you put $20 on the receipt tip line, that is what they will charge to your credit card. If you wanted to leave a $20 tip in cash, you let that line BLANK. To prevent such a future occurrence, you either let the tip on your credit card, and leave no cash, OR you let the cash and put NOTHING in the tip line on the receipt.

That tip line is what you want the restaurant to add to the total $181.36 + $20.00 = $201.36. It is NOT a line to note how much tip you left on the table. Besides, $20 is not a tip on that large of a bill; it's an insult. You have no case to challenge the additional $20 charge on your bill.

you should NOT have put anything for tip on teh CREDIT CARD RECEIPT - of course it is going to get added and a $20 tip on a $180 bill is cheap - that's like 11%

If you left a "cash" tip you should not have entered it on the credit card slip. It is your error and you left a total tip of $40 which is not really too much for a $181.10 bill.

YOU wrote the $20 tip on the cc receipt, so your cc will be charged the $20

if you foolishly left another $20 cash that is your problem.

YOU wrote the $20 tip on the cc receipt, so your cc will be charged the $20

if you foolishly left another $20 cash that is your problem

No.

You added $20 to the credit card receipt = so that makes it $201.10.

Then you left an additional $20 on the table...

By writing $201.10 on the receipt, you authorized that much to be charged to your credit card.

I'm sure they appreciated the extra $20 in cash, too.

Update: In the future, don't also leave a cash tip. The tip goes on the credit card receipt.

In the future, if you tip in cash, then you do not write the amount on the receipt. You either tip in cash OR write the amount of the tip on the receipt. You do NOT do both. You write it on the receipt ONLY if you want to use your credit card for the tip.