For me it is when companies/services market themselves as donating to XYZ cause if I buy their product. If they want to donate, they should have already done that with the money they have. Asking me to give them profit so that they can donate is so obviously pretentious.
There's a pest control salesman who goes door to door every year, who I can't stand. Not only does he say outright incorrect things, but he can't take no for an answer. Every polite refusal turns into, "You know what, we can knock 80 bucks off that right now" or "How about we just make the first month free."
Next time he comes knocking, I'm going to be immediately upfront. I'm not interested in paying money to spray poison, that will end up in the canal and the river, to kill bugs that birds and frogs and bats could be eating.
Next one that comes to the door, I'm telling him he can have $20 if he humanely escorts the Latrodectus Hesperus living in our cupboard out. Let's see if he has any tricks up his sleeve other than poison.