it means that the person bein called inhumanly smelly either has bad body odour or is just being made look bad in front of other people.
Brad:''barry,the smell of u is inhuman!''
Brad:''u smell bad''
-Group of people just standing around.one of them shouts to the other,''The smell of u is INHUMAN''
the group looks at the shouter with a weird look.
shouter:''its a joke''