Francois said:Yeah, for instance.
In some shops/businesses I would not find it out of place. Of course you would not say that to someone who cannot cut a slice of pizza.
Francois said:Well, for one thing you would say that if someone called you or went up to you in the first place, but it is not suitable to propose unsollicited help.
Furthermore, it can come across as a bit "pedantic", which is probably a bit too much for your playful sarcasm.