We all know scenarios that happen in the same way over and over again. Some are funny, some are serious. Let’s share your unwritten rules about your hero or the game in general.
I will start:
Widowmaker- whenever you see an enemy Widow the match suddenly turns into a 1v1 deathmatch and nothing else matters anymore.
Sombra- when you see a McCree flanking you follow him in stealth and wait until he ults to hack him. Or solo EMP for extra salt
I’ll go.
If two Doomfists meet, it becomes a Dragon Ball fight. It just has to.
Also the Moiras that will beam each other until they die, so forever.
If you see the enemy Mercy and you’re playing Mercy, do everything in your power to kill her and then tea bag her corpse.
Always happens when for me but it’s always ennemy moira attacking me, i know it will take forever so i’d rather go for the ana/mercy.
When ennemy moira attack me, eithe i’m out of cooldown and low health and she win. If i engage her, it’s because i have a revenge to take and she doesn’t last long, even with all her cooldowns… I can even withstand her coal… she’d better run…
Wait to sleep/hack a pharah or mercy when either are over and edge
When one Reinhardt finds his enemy counterpart, they play mind games against each other, trying to bait the other into wasting Shatter. So funny to watch
In queue, if someone’s friendly, you don’t have to be friendly too, but it’s rude to kill them (not to mention if they fight back they’ll probably win)
When both Winstons use Primal rage and they either ignore each other and play volleyball with enemies or they just keep booping each other.
Oh my god yes, I always feel psychologically bullied!
Always combo a string of shots as Lúcio with a Boop, despite melee doing more damage and not moving the enemy out of harms way.
Whenever there’s no good opportunity to use Halt as Orisa, just Halt the enemy tanks and say you’re slowing their approach.
If I ever see a symmetra not stacking turrets, they’re new… or bad
there are some situations where you shouldn’t, but normally you should just stack them
Any - You see that you’re not playing the best hero for the scenario. If what you play atm works well then you keep at it, but if you keep suffering you switch heroes 
My favourite is a winston 1v1 resulting in primal rage being used by both and then both leaving as the primal rage runs out.
As Ashe, your goal is to get more Bobs and Bob kills than enemy Ashe.
As Tracer, you are required to say hi before/while dueling the enemy Tracer.
If McCree or Widow instagibbs you at the beginning of your nano boosted blade then you are required to get off Genji.
If you are Hog and come up against another Hog you must try and hook each other and continue to unload entire clips into each other.
Even if either of you decided to use take a breather, you must continue to point black shoot, no matter what.
Or is that just me?
FFA Hog & Moira - you tbag their corpses no matter what
Zarya: If an enemy Mercy valks and goes battle-Mercy, I will grav her to a wall. I ain’t having any of that.
Rein: If one Rein uses the beer voice line, both of them must start spamming that and hello.
I do this no matter what hero I’m playing tbh
If on Reinhardt 360 shatters, it now must be a 360 shatter battle the rest of the game
Lucio v Lucio battles only decisively end with an environmental kill.