Percy met Penelope in the library: the place you'd expect to meet a Ravenclaw, really. It took him a week to work up the courage to talk to her, and then it was only to ask for help with his Arithmancy homework.

It was Penelope who finally got tired of waiting, and asked him out. He was so surprised he almost said "no". Fortunately, he got control of his voice just in time, and said "of course I will".

She turned out not to be a stereotypical stuffy Ravenclaw at all. Oh no, Penny was much more adventurous than that.