A man who is wearing a hat in every picture of his online dating profile and thus hiding the fact he is bald. Only for the unsuspecting woman to find out about said baldness in real life.
‘I went on a date and he was bald’ surely you already knew this prior to the date? No he had a hat on in all his pictures. ‘Oh no he was a hatfish’
A hatfish is a boy or girl who looks very good when wearing a hat, but when people see them without the hat its like they're a completely different uglier person.