Next time you're at that fancy grocery store feeling cash-rich, maybe opt for something besides flavored olive oil. Yeah, the bottles look all pretty and sophisticated and you think maybe when people come over they will "ooh" and "aah" at your gourmet pantry. But trust us: It's not worth it.
Flavors can mask defects, so you can't tell if the olive oil you're buying is any good. What's more, though, is that flavored oils are often home to chemicals rather than pure extracts. (In particular, you're likely to find truffle oil that is made with chemical compounds rather than actual truffle.)
You're simply better off starting with an olive oil you know you like and infusing it with flavor yourself. Start off with a small batch so you don't waste any. After all, how often are you really going to use rosemary olive oil? Plus, the longer a bottle sits, especially exposed to sunlight and the heat emanating from your stove, the faster it will lose its luster.
It's easy to do. Warm your olive oil to 150°F in a small saucepan, take it off the heat, and then add your star ingredient (herbs, citrus, etc.). Let it steep in a covered container for about it a week. It'll get stronger if it sits longer, of course. Here are some recommendations for flavors we like and what you might do with them.
Olive oil + jalapeño: Put it on popcorn
Olive oil + garlic: Use it to fry an egg
Olive oil + rosemary: Coat potatoes for roasting
Olive oil + lemon: Drizzle over fish
Or instead of infusing your olive oil, you can always let your olive oil infuse something else: