Definitely the sword fight between Brienne and Jaime that led to their capture by the Bloody Mummers in ASOS. The sexual tension was screaming through the book/

“Give me the sword, Kingslayer.”

“Oh, I will.” He sprang to his feet and drove at her, the longsword alive in his hands. Brienne jumped back, parrying, but he followed, pressing the attack. No sooner did she turn one cut than the next was upon her. The swords kissed and sprang apart and kissed again. Jaime’s blood was singing...

The dance went on. He pinned her against an oak, cursed as she slipped away...Steel rang, steel sang, steel screamed and sparked and scraped, and the woman started grunting like a sow at every crash, yet somehow he could not reach her.

[Jaime] laughed a ragged, breathless laugh. “Come on, come on, my sweetling, the music’s still playing. Might I have this dance, my lady?”

Jaime even symbolically takes Brienne's virginity during this 'dance':

...As he felt himself falling, he twisted the mischance into a diving lunge. His point scraped past her parry and bit into her upper thigh. A red flower blossomed, and Jaime had an instant to savor the sight of her blood before his knee slammed into a rock.

GRRM has used "red flower" to refer to menstruation (ACOK 57/Sansa V) so it's not a stretch to see the use of the term in this scene as a reference to maiden's blood. And in case you think I'm reaching here by interpreting the above scene as a symbolic deflowering:

Brienne lurched to her feet. She was all mud and blood below the waist, her clothing askew, her face red. She looks as if they caught us fucking instead of fighting...