What a load of self-serving soft nationalistic exceptionalist nonsense.
We don't have the greatest sense of humour in the world.
Neither do we have the best TV, military, queues, police, landscape, weather, manners, way of life, sense of justice etc in the world. All things that British society tried to teach us growing up.
Firstly, we don't have one single British sense of humour. We have a variety of modes of humour, from Jim Davidson to Judy Love to Victoria Wood to Reeves and Mortimer to Last of the Summer Wine to Carry On to Peep Show to pantomime to Stewart Lee.
Secondly, our humour, like all nation's humour, is shaped by us and for us. The things we find most funny are ourselves, our habits, our stereotypes. Of course British people love British humour best. It's what we know. It's who we are.
That doesn't mean it's "the best". It means it's the best for us.