I've always found the lounge staff to be excellent in Admiral's Clubs. They've always been polite and helpful, and offered drinks vouchers.
I've never had a problem with the bar staff, even when they've been super busy.
I've never seen this in ACs, but I have seen it and heard of it in bars and restaurants in tourist areas. Staff can be somewhat cold towards people with British accents, in anticipation of being stiffed on the tip. It's happened to them too many times before.