It’s been a celebrity-photo-filled weekend, as the stars descended on Washington for the annual White House correspondents’ dinner. Roughly 500 miles away in Greenville, South Carolina, Amy Schumer reportedly had a run-in with a fan whose over-aggressive selfie tactics led the comedian to declare that she would no longer take pictures with people.

So, when is it OK to approach a celebrity for a selfie? We’ve put together a brief etiquette guide.

1. Assess the situation. If you're at an event like the WHCD, chances are the celebrities in attendance will have a reasonable expectation that they will be approached by fans. Key word: reasonable. Don't demand a photo or take one without asking. And if it's the end of the night, understand that even celebrities experience selfie fatigue.

If you happen to spot a celebrity while you’re out and about, consider your setting and what else is going on. Is the star in question having dinner with family? Forget about it. Is he or she on a jog or a bike ride with Leonardo DiCaprio? That selfie is probably not going to happen.

If the celeb is casually walking down the street, it’s a gray area. Weigh the importance of this particular celebrity interaction.

2. Be polite. We can't stress this enough. Yes, celebrities choose to be in the public eye, but just like us, they deserve work-life balance. Don't demand a photo or conversation, don't get too hands-y or offer an unexpected hug. You may feel like you know this person from television or films, but in reality, you're complete strangers.

3. Get permission. On Instagram, Schumer wrote that the fan startled her and "put a camera in my face," and when she asked him to stop, he said, "No, it's America and we paid for you." The fan in question told Greenville's Fox station that he was with other fans and that he approached her "in a non-threatening way," ceasing to record when she asked him to stop.

The lesson here is that it’s best to ask if a celebrity wouldn’t mind having their photo taken.

4. Be time-conscious. If a celebrity agrees to take a selfie with you, don't try to wrangle a photoshoot out of it. Take your (approved) selfie, say your piece (I loved you in "Trainwreck!") and move along. There are exceptions, of course. If you're having a lovely, two-way conversation, let it run its course like you would with anyone else. Chances are, if you treat them like you want to be treated, they'll reciprocate.