When someone offers to treat you to dinner, they are usually doing so to show their appreciation or affection for you. Whether it's your birthday, a job promotion, or an anniversary, being treated to dinner is a fantastic way to spend a night out on the town. Many times, however, people equate being treated to dinner with being treated like royalty, but this, my friends, is hardly the lay of the land.
"Go ahead, pick anything you like!" For starters, it does mean to enjoy yourself and order a meal that you do like. But there is a certain level of tact involved with ordering anything you like. Here's the quickest tip: Never order the most expensive thing on the menu.
The same thing goes for drinks. Alcohol is easily the most widely upsold item in the restaurant/bar industry. What this means is that a six pack of Heineken (a higher-end beer) costs less that $10 at a liquor store, but that a single bottle or glass of Heineken ordered at dinner may cost $6 to $7, more if you’re in NYC or Las Vegas. That's a rip-off. So when someone says to pick out a bottle of wine to share, you should choose properly by not picking the one with four zeroes tacked to the end of the price. As I said with the food, do choose something nice, but do not make the person feel they need to get drunk before the bill comes, just to soften the blow.
And lastly, when the dinner wraps up, always offer to either buy dessert or pay the tip. Always, always, always offer! You may be turned down but be persistent. You may get turned down again but still press the point. If your treater ultimately declines, which will most likely happen, always make sure to over-thank the person for their time with a follow-up letter and offer to return the favor in the future. Generosity should always be rewarded.
In the end, when someone offers to treat you to dinner, it's an incredible honor you should greatly appreciate. And order what you want within reason — you do not want to be the subject of a conversation they have later that goes something like, "Well, sure I said I'd treat but they ordered a $125 entree and $800 bottle of wine!… Had I known that I would have taken them to TGIFridays."