Why do tourists think the British have terrible diets (eating sausages bacon for breakfest) and also think British are lazy people?

I don't think the British are lazy.
But I've got quite some British friends, and they are almost all bad cooks with a high amount of grease in their food. I don't think that goes for all the British, but it is pretty much a cultural thing to have your breakfast with bacon, eggs and sausages, floating in grease..
Well, I'm Dutch, and in my country it seems standard to always eat potatoes with loads of gravy, a piece of meat and vegetables. Typical Dutch diner. Thankfully that is changing!
These are just average cultural things. Stereotypes. Which you can never apply to all people from one country. I bet there are countless British who don't eat the typical breakfast, just like there are countless Dutch who hardly ever eat potatoes.
But open up an old fashioned cookbook from England, do the same with an old fashioned cookbook from for example Greece, and count the differences. There is still something like a cultural heritage, also in food. It's where we come from, and for many people this is still pretty deep in their patterns.

Spent four months in Colchester, and I have to say that the food I was treated to was APPALLING. The only thing that was any good was steak and kidney pie, which I ended up eating three times a day.

I went to London to visit a friend. On Saturday, he was busy, so I went shopping with his wife. She bought an incredibly nice piece of beef- even as an American I was impressed with the quality. She also bought some very nice fresh peas.

On Sunday morning, I got up, and she was in the kitchen cooking. She had two HUGE pots of water boiling on the stove, and I wandered what that was about. She had shelled the peas, and got out the piece of beef and put it on the counter top. I thought that was strange, because her husband and I were going to be out for the next eight hours or so. Then she just plunked the beef in one pot of boiling water, and the peas in the other. I was mortified.

That evening, we had over-boiled beef and over-boiled peas for supper. The worst part, and the part that really convinced me that the English are hopeless, is that she added GREEN FOOD COLORING to the peas to make them green, because she had boiled all the green out. The worst meal I ever had in my life, and the sad part was that that poor cow died for nothing, not to mention the poor peas.

I didn't think they were. I never heard such a sterio type before.

Britain is nothing but mere horror.
People are extremely rude and hostile and they do not even know how to be polite.
They offend you instantly if they hear you are a foreigner and you can be glad if they only beat you.
There food is incredible and looks not only like puke but it tastes like puke.
And they are absolutely not helpful and the most often you hear that is "get lost".
A complete nightmare and I am glad that I had to go the last time in my life in 2009 to that strange and hateful country.
If they see a car with a German number plate you almost can be sure that they burn your car over night.
So Germans won't dare to visit Britain by car.
And they are indeed lazy bones but as lazy they are the more arrogant they are.
Nowhere in the world I ever met such an extreme xenophobia as you meet in Britain at each spot and hundreds of times in your daily life.
A visit to Britain is always an extreme risk of life.
Even in Afghanistan where no Brits were around I felt safer and treated better.

The average Briton has toast and/or cereal for breakfast. If you want to see an example of a truly unhealthy breakfast check out the opposite side of the Atlantic and have a stack of pancakes with maple syrup, fried bacon, eggs and goodness knows what else.

They should eat the way the British do - in Indian or Chinese restaurants. :)

Actually if there's one meal when it's reasonably ok to eat fatty stuff, it's breakfast. In any case, nowadays you can get most diets in most places. It is said that the best Indian curries in the world come from London.