Just some post-Avengers babble. Actually wrote this a year ago and forgot about it until I stumbled across it today. Black Widow/Hawkeye.
Disclaimer: Just playing in the sandbox for gits and shiggles, and I'm broke, so please don't sue me!
What's in a name? She has had so many of them - Natalia Romanova, Natalie Rushman, countless cover names for various assignments, but for now she's pretty happy with Natasha Romanoff.
Almost everyone at SHIELD calls her Agent Romanoff, seemingly afraid of getting less than formal with the famous Black Widow for fear she might make them disapear.
Her fellow Avengers call her various things - Steve still insists on calling her ma'am or Agent Romanoff, even though she has asked him to call her Natasha. Bruce has settled with Natasha, as has Thor when he doesn't refer to her as "a maiden fair with flaming hair", which makes her smile inside even if she doesn't let anyone see.
Tony Stark, perpetual pain in her ass, often calls her Natashalie. She would normally kill him for it, but she knows now that he means it in good fun - kind of like his smart-assed nick names for everyone else on the team. She makes no guarantee for his continued existence if he keeps calling Clint "Legolas" though…
Clint Barton. Hawkeye. Lethal assassin, automatic winner of any game involving any sort of projectile (ranging from arrows and bullets, to Nerf darts and rubber bands), and her partner. They had as many names for each other as there were situations they had been in.
During the day when they were at work it was always Agent Barton and Agent Romanoff, blank faced and all business.
On missions with a team they shortened it to Barton and Romanoff, or Hawkeye and Widow.
Missions that were just the two of them he was still Barton, but she was Nat.
But when they were alone in the dark, with no one around to hear, they were simply Clint and Tasha.