to not get why people on MN write "sleb"

[RubyRedRidingHood]

Is it suppose to be funny?

I just don't get it. I find it a bit cringey

Why not just put celeb? It's only one letter more...

It's just a mumsnet "thing" I think, like vaire, naice, dere etc - slightly self-deprecating possibly?

I love it hahahahahahahahaha

Well, it's in the Oxford English Dictionary so why not?

If you don't like it, don't use it!
Simples

It's not a MN thing, it goes back a good few years now. See the Oxford Dictionaries website oxforddictionaries.com/definition/english/sleb

I've always read the word as meaning that the person in question is a celebrity only in their own mind and in the minds of the red-tops; they haven't actually done anything that they would be celebrated for?

I've definitely seen it elsewhere, as WhereYouLeftIt says, it tends to denote a certain type of celebrity whose generally famous for, well, nothing much.

Don't you have 'in' words or jokes with family, friends and colleagues? It's just the Internet forum version

It's not just on Mnet or social media.

I read a very good book called Sleb about 8 years ago, twas very good.