I'm sorry but I have to assume you're not British (which is fine, not your fault). You wouldn't survive one day in the jungle of unspoken rules of politeness that is a Tesco queue.

No 'thank you' for a divider? That's a firm mild stare for you

No 'no worries' when people apologise for forgetting to thank you for the divider? Rude.

No 'nonono it was me luv' when people tell you 'no worries' after you apologised for forgetting to thank them for the divider? Are you some sort of sociopathic asshole?