He met her again when he dove behind a wall to avoid a line of bullets and landed facefirst in her breasts.
Ace popped him in the jaw with the butt of her gun, squinted at his face while he clutched it, cursing, said, "Oh, sorry. Didn't know it was you. Hand me a grenade, will you?" then popped up on her knees to fire over the wall.
"What're you doing here?" was the first thing out of his mouth. It beat "Grenades? Where?" by a matter of mere nanoseconds.
"Backpack," she said, ducking back down to reload. "Same as you, probably. Getting paid."
He pawed through her backpack, found a couple and handed her one. "These the nitro-five? That blows up real nice."
She grinned, wolfishly. "Oh yeah. Regular grenades just aren't worth the time. Quick, let's waste these guys."
"Quicker they're dead, quicker we get paid," Jayne agreed. "On three?"
"Quicker they're dead, quicker we get laid," Ace said, and threw him a slantwise look full of promise. "You know how fights make you kinda horny? Three!"
When Mal asked later what in hell he'd set on fire to get that kind of bang, Jayne only grinned.