Great topic!

I've always loved the 'Natasha only drinks tea' fanon. I don't want to be presumptive, but I wrote Natasha drinking tea in one of my very early fanfics (just after the movie had come out), and then I started noticing it in other fanfics too. I certainly don't think my fic was solely responsible, but I like to think I contributed to the fanon in some way. ;)

I've always been a sucker for the friends-to-lovers trope. An oldie but definitely a goldie.