There are probably multiple examples, but here's what I got.

2)Steve gets in a motorcycle accident and Tony helps him through it.
seanchai and elspethdixon: The Roughest Day

4)Tony dies and lives on in a computer as Steve’s only companion.
dorcas_gustine: I’ll remember best of all, all the things we didn’t say

8)Tony is a werewolf.
crimsonquills: Mating Instincts
penumbren: What Lies Inside (podfic)

10)Steve takes a truth serum and sleeps with Tony.
valtyr: Truth

11)Tony sleeps with Doctor Doom.
Dunno. That one Titanic fusion is all I got, and I think it's beleeted.
But here's one where Doom kidnaps Tony in order to marry him
valtyr: Some Assembly Required

15)AU: Tony and Steve are high school students.
settiai: Avengers: High School's Mightiest Heroes

18)Tony tries to impress Steve with a signed baseball.
Dunno. Steve has an awesome signed baseball in canon though.

19)Tony teaches Steve to dance.
Dunno. Steve knows how to dance just fine in 616.
Here's one where everyone else teaches Steve to dance, or tries to.
valtyr: Team Building Activities

20)Steve takes up knitting.
I argue also canon, but
Kaitou: Five Times Steve Knit Something, and One Time He Refused To

24)AU: Tony and Steve are college roommates.
Dunno.
But here's one where student!Tony models for ast student!Steve
tsukinofaerii: The Billionaire Hooker's Deceived Artist