She had no idea how kinky Barney was.

That one night they'd shared was more about comfort and tenderness than raw passion and need – though even once the secret was out, Barney had sworn her to secrecy on that particular point.

Barney Stinson didn't do cute and cuddly.

What he did do, apparently, was get off on being treated like Robin's bitch.

The first time was an accident.

They'd been lying in bed after a thoroughly satisfying encounter, Robin's satiated body draped across Barney's. She was beginning to feel a little uncomfortable with the intensity of adoration in his eyes, when he broke the barely awkward silence with a soft, awed statement.

"You know you really are the best I've ever had, Scherbatsky. And trust me. I should know."

She had to break the solemn mood that seemed to be descending, so she gave him a teasing smile and retorted, "Well at least all your years of slutting around were good for something."

She was surprised at the slight stirring she felt against her thigh, and her eyes widened in wonder and amusement as Barney flushed bright red, averting his gaze. She repeated the word in a lower, more deliberate tone, studying his reaction…

"Slut."

…and was rewarded with a very definite response pressing against her bare thigh, as Barney's breath quickened slightly and his eyes met hers, dark and hooded with desire.

That single word was only the tip of a very dark, very dirty iceberg.

As their affair intensified and Barney became more comfortable with asking for what he craved from her, the part of Robin that was Barney's best friend worried at the realization that Barney got off on being insulted and degraded.

This can't be healthy. What does this say about his self-worth? He needs help… and not the kind I'm giving him…

On the other hand, the part of Robin that had been attracted to Barney since the first day she'd met him… the part that had wanted to take the arrogant, cocky playboy and break away the façade to reveal the vulnerable, broken boy behind it… reveled in the power she held over him as he flushed and flinched and trembled at her cruel words and possessive touches, all the while impossibly aroused by every one.

She called him names, hissed filthy insults in his ear… even slapped him once. After that, she felt terribly guilty; but Barney swore it was the hottest thing she'd ever done. He laughed at her embarrassment, reaching out to grasp her hand with warmth in his expressive eyes that seemed unusual given the circumstances.

"It's okay to bitch slap your bitch, Robin," he reminded her. "And that was the game… right?"

She nodded, unable to look at him for a few minutes – but secretly proud that she had managed to up the ante, to surprise and amaze and fulfill him once again. She kept trying new things, pushing the envelope, pushing him, seeking the limits to his darkest fantasies.

Then one night… she found them.

"Filthy little whore," she whispered in his ear, slender fingers tangled in his hair and jerking his head back so that he hissed with pain. "Dirty slut… worthless… only fit to be used for my pleasure…"

Barney groaned with mingled pleasure and pain as he reached for her, only to have his wrist caught and his hand slammed back against the headboard. Robin leaned down to claim his mouth in a possessive, angry kiss, leaving him breathless when she drew back to continue her torrent of dark, wicked words.

"Nothing but a pretty little whore," she whispered in his ear, one hand reaching down to stroke him harshly, driving his arousal to higher intensity. "Nothing but my bitch. Good for nothing but to be used up… and thrown away. Sooner or later, I'll get tired of you and move on… because you don't deserve me, slut. You don't deserve me, dirty little whore…"

So caught up in the moment, it took Robin a few moments to realize that Barney had gone perfectly still and silent beneath her, barely breathing. She slowed her motions to a gradual stop, opening her eyes and raising her head to meet his gaze. Her heart skipped a beat when she saw the tears glittering there just before he closed them and turned his head away, a painful swallow visible in his throat.

"Barney?" she whispered, her voice small and hesitant. "What…?"

He shook his head, struggling to speak for a moment before forcing a smile and replying without looking at her. "Nothing… it's fine. Don't stop…"

She went on as he asked, but her words faded away for a bit, then began again – but as words of encouragement and affection. She clung to him, as if afraid that if she let go he might fly away, out of her reach.

And if he does… it's because you drove him away…

Their completion came in silence, and she collapsed against him, holding onto him for dear life.

"I didn't mean it," she whispered at last. "It was just… part of the game." She hesitated, her voice trembling over the words that were still so difficult for her to say. "I… I love you, Barney."

He was quiet for a long moment, before gently pushing her away and rising from the bed. She watched him go, a troubled frown on her brow and a cold sensation deep in her stomach. Her voice was small and meek – she barely recognized it – as she softly murmured his name.

"Barney?"

"Funny," he remarked as he reached for his robe, his voice trembling with quiet emotion. "How easy the other words came to you." He looked up at her, and it was impossible to miss the anguish in those piercing blue depths. "Seems to me… the ones you mean… should be the easiest to say."

And he walked away, leaving her there, alone with the guilt and confusion of her own swirling, troubled thoughts.