How do you interpret "is always being"? Is it grammatically correct to say:
- John is always being generous.
- He is always being late.
John is always being generous.
He is always being late.
Always usually means at all times or every time. You don't use it with a verb in a progressive form in this sense. When you use it in a progressive form, it means "often/again and again", especially but not necessarily in an annoying way. If something is always happening, it happens often.
So both the sentences are grammatical. I don't think the first one shows any annoyance, however; the second one shows that. Look at the following sentence that is indicative of some sort of appreciation:
She's great - she's always laughing and smiling (The Free Dictionary).