We’ve all done it, and there’s no need to feel guilty. “We have this loose rule that if your companion has a ticket and is in the building, it’s OK to save a seat,” says John McCauley, a senior vice president at Loews Cineplex Entertainment. What isn’t permissible, he says, is saving for someone who hasn’t yet plunked down his cash — or draping coats across several seats, which is “what we ethicists call being piggish,” says Randy Cohen, author of The Good, the Bad, and the Difference (Broadway Books, $14 at www.barnesandnoble.com). Claiming the seat next to yours without putting anything on it “creates confusion and suspicion,” he adds, so do use a placeholder. If you’re arriving coatless, bring an expendable item like a newspaper — don’t tempt fate by using your purse. What if someone demands that you give up the seat? If the situation allows, “I volunteer to shift over a seat or two,” says Mary Mitchell, author of Dear Ms. Demeanor (McGraw-Hill, $13). Otherwise, graciously explain, “My friend will be along any minute” — and develop a deaf ear if you must.