Red Nose day is a very British thing. It's an annual charity event on the BBC. It was started by a group of comedians as part of "Comic Relief", in the same vein as Bob Geldoff's "relief" events.
The red nose is of course the symbol of the clown.
People run around all day doing stupid things to raise money. You can buy red noses to wear or to put on your car and so on. All the money goes to the charities.
In my time I have jumped off Bognor Pier, dressed as a ballerina, holding two small propellor fans, in order to help me fly across the English Channel (total failure!).
I have also jumped off one of the piers at Brighton, dressed as a Ronald McDonald. The aim was to fly more than 12 feet. As the pier is about 30-40 feet above the water, I flew that distance. Straight down. People had sponsored me for various sums of money, per foot travelled. Heheh.
Also done a sponsored custard-pie fight. Best fun I've had in years. Fifty of us, throwing custard pies at each other and especially at BBC celebrities. Don't some of them get grumpy?