Dude, for the fastest guy alive, you give the slowest goodbyes.

The Flash:

[the heroes all observe from a high building as the villains are taken into custody by the Gotham police; Flash turns to Nightwing and smiles]
So! Y'know, thanks and stuff for... believing in me. Nightwing:
[a tiny beat before he briefly smiles at Flash]
Yeah. It's cool [he continues to watch the city below them] The Flash:
[still smiling at Nightwing]
We'll have to do it again. Nightwing:
Sure. Whenever. [turns to face Flash now] The Flash:
Because... you know, I really... Nightwing:
[interrupts with a smirk]
Dude, for the fastest guy alive, you give the slowest goodbyes. [a beat as Flash is taken aback. Flash grins then salutes Nightwing before speeding off on his way; Nightwing smirks, then confidently leaps off the building, also departing]