The problem is that so many people use the word vegetarian incorrectly, e.g. as per post 2 already. No vegetarian eats any animal parts, whether they are liquid or have been swimming when they were alive.
For unknown reason, some people choose to call themselves vegetarian although they are not. We need to stop them from doing that since it's ruining the market. 20 years ago nobody ever assumed that I ate fish, being a vegetarian, but nowadays it is not unusual.
If this happens with people you know, could you perhaps bring it up in a lighthearted way at a time when they're not inviting you/not at their dinner. Say, sth like 'I was at x restaurant and it got a bit embarrassing since they did not know that vegetarians do not eat any dead animals' - so kind of mentioning it as an unfortunate incident unrelated to them?
Alternatively, if you're at theirs already, I'd just be bold and say sth like 'I'm really sorry to be asking, but I know there have been misunderstandings before, so I just want to clarify that there's no meat stock, non-vegetarian cheese or gelatin in the dish you've made?" and make it clear that it's not a problem if they have used it (although it is of course a problem...). So if so eat what you can and smile.
And always bring some nuts that you can eat just in case...
That is incorrect. There are many different types of vegetarians. Your definition is one type, however, that doesn't make other definitions less valid.
The point is that if one has specific dietary restrictions, they need to make sure those are communicated properly or should eat something prior to attending to ensure that they don't starve if nothing they can eat is served.
Please show me any evidence from a recognised source that states that the word 'vegetarian' can be used for a person who consumes /pieces of/dead animals?
Here is the NAVS definition:
Vegetarians are people who abstain from eating all animal flesh including meat, poultry, fish and other sea animals. An ovo-vegetarian includes eggs, a lacto-vegetarian includes dairy products, and an ovo-lacto vegetarian includes both eggs and dairy products. A total vegetarian (vegan) consumes no animal products at all.http://www.navs-online.org/faq/index.php
International Vegetarian union:
Vegetarian: IVU defines vegetarianism as a diet of foods derived from plants, with or without eggs, dairy products, and/or honey.
Those using eggs and/or dairy products are often known as ovo- and/or lacto-vegetarian.http://www.ivu.org/faq/definitions.html
And here is the UK Vegetarian Society definition:
The Vegetarian Society defines a vegetarian as: "Someone who lives on a diet of grains, pulses, nuts, seeds, vegetables and fruits with, or without, the use of dairy products and eggs. A vegetarian does not eat any meat, poultry, game, fish, shellfish* or by-products of slaughter." http://vegsoc.org/page.aspx?pid=698