Off the back of my previous thread Things you never knew were vegetarian? http://www.mumsnet.com/Talk/foodandd_recipes/3566566-things-you-never-knew-were-vegetarian
As suggested I am asking the reverse question!
What food items/products have you discovered that you would expect to be vegetarian friendly but aren't??
The Worcester sauce thing was a revelation to me, I already knew about cheese and onion crisps.