My experience has been that they don't make a general announcement about a free drink but don't charge you for it if you order one. At least thats whats happened with me on my last couple of flights that were delayed. It was the same for the headphones. I noticed they just handed them out to the passengers that requested them but didn't charge them, although no announcement was made to that effect.

(As an aside, flirting seems to be a great way to get a complimentary Baileys, delay or not!!!)