This letter is to someone whom you just met and who you want to see again...but whose name you just can't recall.
Hi! I really had fun <time> at <place> and enjoyed spending time with you. I was wondering if you might want to go out, but first I have to ask a really embarrassing question: What's your name? I <reason you can't remember>, but I can't remember. I feel really stupid, but I do like you, so could you please give me a call and tell me your name? If you think I'm a jerk and never want to talk to me again, I guess I can understand. But I hope you'll call. Thanks.