Mycroft Holmes was, by all means, a measured man. His words were carefully chosen, to achieve maximum effect with minimum effort. His clothing was tailored to suit the image he wanted to project, and his expression was constantly being schooled into the appropriate mien for each situation.
That's why John was shocked to hear that Mycroft Holmes could, and did, get drunk. Granted, it was only the one time (that Sherlock knew of), and that had happened over two decades ago. Mycroft had been home from Uni for Christmas, and had, in a fit of insanity, decided to drink his troubles away. (On that occasion, it was the Holmes family, both sets of grandparents, plus Uncle Rudy and Great-Aunt Myra all in the same room at once, so he couldn't really be blamed.)
"It was an occasion to remember," Sherlock chuckled as he reminisced. "All I need to do is say 'Christmas 1995' to get Mycroft blushing."
"Mycroft is biologically incapable of blushing," John stated. "I'm pretty sure he's just some scientific experiment gone wrong, dumped onto you by your crazy Uncle Rudy."
Sherlock shook his head firmly. "You don't believe me, do you? I'll show you the next time Mycroft comes over. Have a camera handy."
John couldn't wait even a bit.