Unless it's someone at the beer garden who wants you to clear the table and bring them another, this sort of call is more trouble than it's worth.
It's generally said in a semi-agressive way - whether the speaker is known to you or not. It demands that you are impressed and appreciative of whoever has just shouted it out based upon the fact that they are worth seeing. It's also often based upon that first pitcher of beer. Failure to comply can be dangerous, but shooting the picture can be trouble too.
In the old days the shouter would generally forget all about you once they had posed and grinned or made a rude sign or whatever - now they demand to see the screen on the back of the camera to see how great they look. If they are not pleased they demand another and another. The real horror is when they demand the images be sent to their mobile phone account so they can plaster them onto social media. unfortunately camera makers are making this all too possible these days - many options exist to do just this.
If you're a paid shooter or working for images that you'll offer for sale it is downright imposition and nuisance and dilutes any professional work that you're trying to engage in. The best you could do in many cases was pretend to be deaf and move off into the crowd.
But there is a way out of it. All you need is one of the small Fujifilm Instax or Leica Sofort cameras and a pack of film. The cameras do the 90 second in-the-hand instant print and are so automatic that you really need spend no time at all setting them up. You can sling one rond your neck or have it in the camera bag as you work other cameras.
" Hey! Take My Pitcher! " goes off and the drunk lurches in front of you while you're setting up the event or wedding shot. If Security doesn't get them quickly it can be trouble, so just whip out the Fujifilm Instax or Leica Sofort, pop one flash and then put the developing print into the pest's hand. They will be so occupied for 90 to 120 seconds that you can get the shot you originally started for - by the time it's developed in their hand you're off and away.
Even if they or others continue to pester you, they will stop after the 10-pack of film is exhausted - even drunks can understand an empty camera - and their minds will not return to thinking about the rest of the digital gear round your neck. It costs a little, but it is like those decoy flares that airplanes fire off when they are landing in war zones - a sacrifice to keep the drunks at bay.
Note: If you do get stuck with taking digital images and they keep pestering you to see the LCD screen, be aware that they will reach and grab as well. And then demand that you delete the images that they don't like. With professional work, deleting in the midst of a swirling event mess is just asking for trouble.
One ploy that works when they start up is to say that you have to go change batteries or cards and need to do it in a dark place. Then just move away and don't come back. In the worst cases, you might have to move interstate.