It is debatable which nationality has the greatest sense of humour, because humour differs according to national quirks and traditions.
It will no doubt be agreed by all, that the majority of humour results from suffering - usually someone else's suffering. This unsympathetic trait afflicting the majority of mankind is nevertheless a rich and often pleasurable source of wit and sarcasm. But the very best humour comes from the antics of youth pretending to be mature and wise.
Place anyone in a difficult situation in an unfamiliar environment and you have the perfect script for a comedy sketch. I have had plenty of experience in this area and can testify to it - 'both feet first' tends to become 'head first' without any effort or assistance whatsoever.
I am a Yorkshireman - Yorkshire is a large County in the UK (this information is for our American friends who seem to think that the UK is part of London) - and in general we consider our humour to be the best. We laugh at ourselves and everyone else whenever possible; we are also grumpy by birthright and we never miss an opportunity to exercise it - as anyone who knows Yorkshire folk will confirm. Our humour has been developed over many centuries, enriched by our forefather's efforts to conquer the world and the suffering for the majority of the British population that followed as a result.
As for the humour of foreigners, I have to admit that I often find it difficult to understand American humour, which on the whole appears to be governed by sound-bytes. There are exceptions of course and the American political scene is a rich source of fodder for us to exploit.
Russian humour appears to be very much like ours, no doubt born out of their long suffering under communism, but the Germanic peoples that I have met seem to lack it completely or are just afraid of it. Asians (from the Indian sub-continent) have a good sense of the ridiculous but are very sensitive to criticism when they are the targets, however humorous. The Mediterranean nations have fiery temperaments and tend to take themselves far too seriously. But let's see how the site develops and I invite everyone to join in the fun.
The root of good humour is definitely the ability to laugh at ourselves first and foremost and then we can laugh at others with complete abandon.
If you want to add to this, you can do it through the forum and I'll include it.