To spin a dit would be to make a claim about an event which is usually extravagant but you, in your own mind believe is legitimate and such an erratic story will perhaps boost your street cred. Most other people with you will realise the nauseating exaggeration of such a story and tune promptly out.
Chris: Thats a nice house.
Mitchell: Yeah thats the same house at which my dad defused a bomb.
Chris (to companion that isn't Mitchell): Here he goes spinning dits again.