Natasha has a habit of coming up behind Bucky and putting his hair up for him whenever he's doing something and his mop of hair gets in his eyes. Whether he's trying to figure out the computer or eating or bickering with Steve, she'll just sidle up behind him and pull his hair away from his face in a little half-bun, and he just holds still until she's done because, honestly, everything is so much easier when he can see.
Bucky is the one person Natasha allows to sing with her. I can imagine Natasha introducing Bucky to popular music from now and they start rocking out to Fall Out Boy. Meanwhile, Bruce is trying desperately to convince Tony not to record it, because he knows that if Natasha finds out, she will murder on the spot.