To express indignant disbelief at another's fanciful proclamation.
Typically accompanied by the stroking of a non-existent goatie beard.
For some reason "reckon" is pronounced "reh-kon" rather the usual "reh-kun".
"I managed to cop off
with 5 birds on Saturday night."
"5? Chinny reckon."
This means 'yeah right' or 'I don't beleive you'. It is pronounced 'chinny re-kon' and has more impact if you say it whilst stroking your chin. We used to say it at primary school, but it might just be a Northern thing!
"You get £100 pocket money a week?"
Up until around the age of 12 this is a common phrase in every child's vocabulary. Used to question the validity of somebody's statement. In cambridgeshire there were two variations of chinny reckon or "Chinny Rah-Kon". Firstly one would put their tongue imbetween their bottom teeth and lip, making it swell, and make a low noise before saying "Chinny Reckon" or "Itchy Chin". The phrase "Chin Spin" was also used in the same context.
"I've scored twenty five goals on the playground this week"
"Yeah, Chinny Reckon"