Get a little sarcastic and tell her she should stay out of your love life.

You smirk at your sister, "Hmm... you said 'any of us', Abs. Does that mean you're including yourself with all those girls who would be crazy about me? Because from what I've seen, pretty much every other girl is fine just ignoring me. By my count, so far exactly one girl has shown any interest in me now. My own sister." You say with slightly bitter, sarcastic bite to your voice.

You sigh as you look at her, and your tone softens. "Look, I get that you're just trying to be a good big sister and watch out for me, but you're putting more effort into my social life than I am, and it just points out what a loser I am that you have to be so worried about me. It makes me feel even more like a freak. Like, I'm 18 and never kissed a girl, so my big sister has to step i..."

You are cut off mid-sentence, when Abbie leans in and kisses you right on the mouth. Her lips are warm and soft against yours. It's not a quick peck from a sister to her brother, either. The kiss lingers. Her hand moves into your hair, fingers running through it. Her fingernails scrape lightly over your scalp. Then she surprises even more when the tip of her tongue teases between your lips and into your mouth. You are too stunned to respond at first, and just passively let her kiss you. After a few seconds, you just barely get up the nerve to let your own tongue circle and slide over hers. Then she moves her mouth away from yours and to your ear. Her full lips brush your earlobe. You can feel they are now slightly moist from the kiss. She whispers very quietly. "You're not a freak, little brother."

She leans back, looking at you with a broad smile. It's very different from the taunting grin she wore all those times she's teased you about girls. The expression on her face looks like pure joy. "But that doesn't mean we can't be a little freaky." She giggles.