Why does it have to be an NPC? I play on an RP server, the last year or so my character and another have been trying to keep their hands off each other because the other person is already involved and has a child with someone. It's great fun playing it out, though nothing girlfriend-y ever really comes of it.
My guardian druid (in bear form) would love to know li li a little closer. I swear she said she's 18 !!!!
My blood elf hunter would go for loli version of herself. Playing with yourself brought to next level.
My Dk... well.... ghoul with boobs ?
I sometimes play a gnarly old orc warlock; almost completely bald ontop, stiff wirey white beard all the way down to his waist, hunched over and gangly from age. I'm talking First War "Orcs vs. Human" veteran kind of old. One day while passing through the Blasted Lands he ran into an old war "friend", Lady Sevine, only she was still young and vibrant as they had been long ago.
She convinced him to stay awhile. They stayed up all night reminiscing about the war, the differing paths their studies had taken since then (she showed him her latest book, he found it a bit too heavy on symbolism), summer nights spent in Nagrand before the world was sundered. She told him about the new master she served, and how the Burning Legion rewarded its servants in ways that Thrall's Horde never could. She promised him the vigor of his youth back, tantalized him with secrets of demonic powers straight from the source, and of course, a respite from the bitter loneliness of his venerable days. All she asked in return was his soul.
He gave some serious consideration to her proposal, then slew her with an enchanted weapon and drew her soul into a shard. To this day he still keeps it close to his heart; not out of sentiment of lost love, but as a bitter reminder of the fate of those who sell their souls to the Legion.
Uh.....I play a male dwarf, so I'm not too sure what would best fit there. I guess one of those Dark Iron chicks in the BRD bar. Or that one female dwarf who keeps running through Ironforge screaming about bread for sale.
Also I play a couple of male human characters, in which case one of those hot female villians in the slutty/revealing outfits (Vanessa Vancleef, Whitemane, etc) would do.