I did once have two quad espressi while waiting for a flight at stupid o'clock in the morning at Stansted airport. The guys in Costa coffee mostly just found it amusing.

I was also once approached by an alcoholic who chastised me for drinking coffee in a bar in the middle of the day instead of "a real drink". I offered to take a shot of vodka for each espresso he drank and "we would see who dies first". He didn't take me up on my offer.