Tony:
You would call him Metal man, based off what Thor would call him. You weren't exactly sure if he liked that name or if it annoyed him at all.
Tony would call you Baby or sometimes Babe. Honestly, this is Tony Stark we're talking about.

Steve:
You enjoyed calling him Capsicle. Steve at first was quite annoyed with the name, but he soon got used to it.
Steve would call you Sweetheart or Darling. Occasionally he would accidentally call you Peggy, and he would apologize for it faster than you could reply.

Bruce:
You called Bruce the same thing he called you; Darling. When you said it, you said it with a very calm voice so he wouldn't take it the wrong way.
Bruce would call you Darling. For the most part he would call you by your first name, but whenever you heard him call you Darling, you knew something was up.

Clint:
You would call him Katniss or Legolas. (Does this really need much more of an explanation?)
Clint would call you Honey. There's not really anything much more to say about that.

Loki:
Your Highness or My King. Loki loved being treated like royalty, especially by you.
He would call you my Queen. You had to admit, you loved being treated like a queen.

Thor:
You didn't have a nickname for Thor, you just liked his name as it is!
Thor would call you Lady (Y/N), and you loved how polite he sounded when he said it.

If you are reading this from my recent update I changed Steve because apparently everyone is mad at that one. Sorry.