Whenever my FIL is round, I offer him 'tea or coffee?' (hoping he'll say no time for either, but so far not!)
He always says 'whichever is easiest'.
I always say 'they are both instant - one is from a jar, the other from a box next to the same jar, I'll be using the same kettle now FFS* which do you actually want?'
Then he always says 'whichever you're having'.
And then I always say 'I am having water, you have known me for 4 years now, you know I don't have either, which do you want'.
When I'm feeling in the mood, like to say 'I'll just get you a water like me then'. That usually prompts a decision. Oh I know it's not the worst PIL situation on Hitched... but it's such a pantomime! Just tell me what you want man, godammit!!!! <rant over/> ?
*that bit is said in the eyes, to MrMG, not out loud, of course!