At school, it is a habit of some people to say this is haram and this is not a haram etc. e.g the other day someone mentioned that a chocolate is haram.
These people aren't people of knowledge and may just have heard it or looked up an ingredient and found that it is something to do with an animal.
In this case, it may not be haram because e.g. shellac is involved with animals but is is still halal.
In these cases, should you listen to the person and not eat the food or not?