I've only had it refused once, and that was ex-CDG earlier this year. FA was quite off hand about it, like I shouldn't even have asked for champagne. I figured it must just be a French thing...

But they have "run out" of the pink stuff before take off though plenty of times this year, including both sectors I've flown this week. Harking back to another thread, the new brut tastes like a massive downgrade to me on anything served previously. I preferred to wait until airborne and drink something else on the second flight. Might just be a matter of personal taste though...