Tony:

You two argue about who the smartest is. He teached you everything. He always wins by yelling you are a kid and can't even count to 1000. You always cry when he says that though. Pepper always just sighes and asks why he always argues with you. His excuse would be, you started it.

Steve:

You two argue about who runs the fastest. To choose who wins, both go to park. He might win in fastest but you can run more laps.

Clint:

Of course, about who shoots better. He always wins which makes you angry and begin practicing more till you can beat him.

Natasha:

You both argue about what type of gun is better. You choose SMG and snipers but she likes to go with pistols and shotguns. So both mostly argue and try to prove the other guns are bad.

Bruce:

You and him argue about science. Which the others find annoying when you two begin saying words they never even heard of. Tony just would yell he already has the result. You like being right so will still argue even if Tony found out the results.

Thor:

Poptarts. That's all to say. Poptarts.

Who gets the first one, the last one, which flavor, etc...

Loki:

You and him would argue about fandoms. You would force him to read books like Harry Potter and then ask how it was. If he says 'Bad' You would begin saying everything good about Harry Potter. If he says he likes Hobbits more, both would argue till the other finds the book good.

Bucky:

You and him argue about who knows how to drive a motorcycle better. It may sound silly but it's awesome because you can always show him your stunts.

Peter:

You and him argue about grammar. Nobody would think he's a grammar freak but he is. Tony gets crazy when you two argue about it because he finds it silly. At the end Peter always is right so Tony doesn't see the point in this.