I hope this is a troll, but giving you the benefit of the doubt; there is one big flaw in your plan:
Bar codes are nothing more than a representation of numbers unique to a line item. Those numbers are not generic.
i.e. the code for say a bottle of 'Home Farms, 2 litre, semi-skimmed, 2% fat, milk' at Sainsbury, will only last as long as the store does not allocate that number code to a different product. That same code may call up 'de-worming tablets for dogs' in say Tesco, or most likely, nothing at all.
It most certainly will not work in any store other than Sainsbury, and even then, it will only work as long as Sainsbury does not change the code.
In essence, you would be branding yourself forever, with something that has a literally limited shelf life for both the product and bar code. It could work for two years in a Sainsbury store, or it could change the next day.
You could even be unlucky and find the code was changed while you were getting the tattoo, and when you proudly scan yourself for the first time, it comes up with 'Durex, extra safe, 6 pack.'