Have to agree with Phil, sorry Manos on this occasion your completely wrong, one should wear a life jacket or buoyancy aid at all times and especially when pulling off stunts like this, being too hot is not an excuse, what happens if the passengers thrown off the back and brains himself on the A frame as he goes through, the boats going so fast that the driver might not notice the accident for bit, by the time he notices and gets back the face down casualty may be past saving!
Besides this the wind chill at 40-50 knots would chill anyone down enough that a slim fitting life jacket wont matter much to heat retention.
Also have to presume as Niels is in Holland and presumably he's playing in the North Sea with this boat that although the air temp may be nice and warm the sea certainly is not. Not all of us are as lucky as you to live in a very warm climate, most of us have to wear protective clothing most of the year or if nothing else carry it as an emergency, if you ever come on my boat (and your most welcome anytime mate) i'll insist on your wearing of a life jacket and most good skippers would do the same, Hey it might even go with those swimming trunks
Richard