The name is obviously intended to capture attention by incorporating a swearword. It works - I haven't heard of any other random coffee shops in London. But it's also a clever pun that only works if you have the exact non-standard thing that I'm researching right now: a missing preposition!
If you have the standard version of what I'm talking about, you'd say
Let's go to Costaor
Let's go to Fuckoffeewhen you were suggesting coffee places to go to. But if you have this non-standard form, which is found in London and in various other UK places, it means you can miss out the preposition to when you're talking about certain locations or institutions, such as a familiar coffee shop. So you might say
Let's go Costaor
Let's go Fuckoffeewhich, for most people with a native London dialect, will sound exactly like Let's go for coffee.