"There is nothing between them but deep friendship. Sherlock has no sentiments and John is only interested in women.
Sorry, but that's the truth. Since ACD. And ever after. Anyone maintaining the contrary will be punished to watch no less
than three hours of Jeremy Brett." (Source Unknown)
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This quote is funny, because if there is any interpretation of Sherlock Holmes that really makes him seem gay, it's Jeremy Brett.
And in canon, some of the way Watson describes Holmes (physically) would sound like romantic attraction if said today.
Of course, we all remember Mycroft's infamous, "happy announcement by the end of the week," crack, but there is a far more subtle "Johnlock," moment here.
Mycroft: What is your connection to Sherlock Holmes?
John: I don't have one. I hardly know him. I met him (beat) yesterday.
It's that pause before "yesterday." As if John has already kind of forgotten, or has to think a bit to remember, that it WAS only yesterday. As if it's already hard for him to remember his life without Sherlock.
And I think Mycroft's crack is actually a rather realistic crack by one sibling about another...teasing your sibling about someone you think they have a crush on.