Molly Hooper wanted to have coffee with Sherlock Holmes, but he took it as if she was offering to make it for him. He asked for black coffee with two sugars. She brought the coffee up to him upstairs during his first conversation with John Watson.
Sherlock Holmes made coffee for John Watson using sugar pilfered from Henry Knight's kitchen as an experiment to see if the sugar was drugged. John initially baulked at drinking the coffee, since he doesn't take sugar, but took a few sips to be nice, thinking that Sherlock was trying to apologise for his behaviour the night before.
Coffee appeared in the Sherlock episodes:
Coffee was mentioned in the Sherlock episode The Blind Banker.