context man.
I was referring how to fight him in lane.
and if he flashes into you and you flash out your STILL inside his Q range. your gona get a stack, he'll get 5 stacks on you faster and you'll die from his ult.
if you don't have the movement speed to outrun him (and lets face it, he'll have deadman's plate by the time your team fighing so you can't) The optimal play in this scenario is to walk INTO him while his Q is casting, avoid the stack, avoid healing him, and after the Q is cast THEN flash away so you don't get him by anything.
that's the best thing to do if the above scenario happens but tbh your pretty screwed if this happens, why is your support not stunning his dive.
Do as you wish, I've played against him and played as him. noone is taking advantage of this rather large weakness when fighting him.
Fighting darus 1v1 is all about good trading and denying him building his stacks so he can finish you with his ult.
Darius optimally will E you next to him, then auto (one stack), W you (two stacks), then auto(three stacks), Q as you run (four stacks), Then auto (five stacks) and ult you.
He can also flash Q (one stack), E you, auto (two stacks), W you (three stacks) auto (four stacks), Q again (five stacks).
you'll notice with a full combo he can easily get four stacks, the last stack is the difficult one unless he has Q.
If you deny him at least one stack of his passive you have a chance to escape, he only gains 40-200 free AD if he gets 5 stacks. you HAVE to deny him that in a team fight, even if it means you die your team can kill him without him cleaning up the fight.