Some of these replies!!!!!! 
Op didn't ask for opinions on her child's name, she asked if she was being unreasonable about how she wanted to react/handle it, how people were making her feel.
Then a load of replies basically being cruel about her choice of name?! Brian is fine, not everyone's taste, but I've heard absolutely awful names being suggested on baby name threads, Brian is relatively normal as a name, although not very popular at the moment!
What on earth are the responses being cruel about the name op chosen suppose to do for her "your right mumsnet. Let me just go change it"
Op, please ignore those being stupid about your child name, you family are being very unreasonable saying things like they can't say LO name without laughing etc, as for nicknames, we'll that happens all the time to babies - I wouldn't think too much about this, let them continue, but use a firm "brian" whenever you speak about LO, or simply ask if they can just use his proper name.
Baby Brian isn't going to be a baby forever, as a child and an adult, he will have a sensible, serviceable adult name - and in time, people will stop being silly about his name.
Once he is in nursery/school, teachers won't be making names up for him - Brian will stick and this won't be an issue anymore.