It depends on what you mean by "says the word 'Tumblr' in it."
I'd give my attorneys carte blanche to send a C&D to the owner of any service using "tumblr" in their domain name, if that's what you mean. I'd ask them to create a template for me to ok and never think about it again, unless it seemed like they were spending too much money on it or other evidence that they were being overzealous came to my attention.
You are a bully. Do you realize that? Even though a C&D has no direct legal power, it abuses your position of having a nice fat legal fund, and will most certainly lead to stronger charges in any actual legal action.
