Mike,
Yes the papers do misreport and blow up things out of proportion but that's what they do, and that is why people buy them because they like reading this sort of thing. People tend to buy the papers which most closely reflect and reinforce their own views and prejudices. However I rather doubt that the sort of people who head up the RNLI would have found this sort of humour particularly amusing, it's something most people grow out of. But by putting the video into the public domain the people responsible have practically invited the press in and shouldn't be too surprised at the consequences.
Nick,
You make a perfectly fair point that 'boys will be boys' (or girls) but I think it more of an age thing than down to the dangers of the job. The lifeguards undoubtedly do a good job (when they are lifeguarding) but I don't think that in the normal course of their duties they face anything like the hazards lifeboatmen or servicemen/women on active service do. Their job is a responsible one but I would doubt if they regard it as stressful, in fact I bet they enjoy most aspects of it a great deal.
Andy,
Go to the back of the class, you haven't been reading what I've been saying!

It isn't actually necessary to see the video to make the comments that I have. As it happens I did see a number of stills from it when I was Googling to see what reaction to it was and it's very clear just what it was about - been there, done that sort of thing many years ago. As others have said, just average juvenile schoolboy humour. Nothing the matter with that except the context in which it was done.
Colin