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.
Use a different email alias for each site. Duckduckgo with their duck.com, or Apple’s Hide My Email makes that easy; let your password manager keep track of the alias. If they start to spam me, I know not to use that site again, and I can delete the alias so that the spam goes into a black hole.
I use my pets names. They frequently get special invitations for credit cards.