First off, I think that if a guest got annoyed because I was serving something that both he and his girlfriend would eat, they would go to the bottom of the list when it came to accommodations (I'm assuming you mean that the guy got annoyed when always served chicken at your place, rather than meat). If that were the case, I'd have no problem serving seafood
In this case, I'd probably stick with chicken and vegetarian when entertaining them, because that's not too strong a restriction, and concentrate on finding some more variety in recipes (or maybe some turkey, or duck).
However, in a case where the dietary restrictions are really incompatible and restrictive (say you have a vegan, a gluten intolerant and someone with a soy and nut allergies at the same dinner) then I'd either invite people separately, or prepare the dishes so that everyone gets something to eat.
For big gatherings, I would rank the restrictions in order of importance when it comes to what dishes I prepare. Allergies and physical intolerances at the top, moral/religions choices next, and pickiness and dislikes not considered at all.