Why does one not feel pain when having company?

Well first, I’d have to say that some people feel more tense and painful when having company, due to the stress factor. That being said, if you feel less pain while entertaining, it’s probably due to a lovely cocktail of adrenaline and distraction. Nociception (pain perception/sensation) is affected in contradictory ways by, on the one hand, focus, and on the other, distraction. Bradley Voytek and Paul King cover this quite well in their answers to the following question on Quora.com, Neuroscience: How does the level of conscious attention to sensation affect its intensity?

Now, stressful situations put us into the fight-or-flight response by shooting adrenaline into our system. Thus, the more stressed and nervous you are, the more likely you are to get a temporary break from existing painful sensation, otherwise known as “stress-induced analgesia:”

Stress-induced analgesia may be adaptive (i.e. increase survival) by reducing pain from injury and thereby allowing the animal to enact appropriate attack or escape behaviours. It may also be useful in injured animals using immobility or feigning death as strategies for eventual escape from a predator, by reducing pain sensation and associated motor responses, and this may also prevent further damage while the animal recovers from injury. (J4.191.w5)

Neurophysiology of Pain (Techniques Overview)

So, stress and distraction can temporarily relieve you of pain because your body is busy protecting you and making sure that you survive those wacky host-entertainment circumstances. But once you come down from that lovely cocktail of adrenaline and distraction, there tends to be a nasty price. Called a “rebound” effect, the pain once again resumes or even magnifies. This has been commonly observed, but the mechanisms are not well understood or documented scientifically yet.