Go buy a car. Go buy a lot of cars. Go buy a car while pretending to be broke. Go buy another one while thinking you've got a million in cash in the bank. Buy a used car. Buy a new car. (I don't feel bad about consuming car salespeople's time...)
Go to a market in Italy and try to buy anything without haggling. They can negotiate the price of a $10 necklace.
Go to a flea market and find something you want. Try to get a lower price.