lol dude, iv only just started playing the guitar, and already im seeing huge interest init from girls when im saying im taking lessons...

the line iv used when a girls approached me and bought it up is "im not a lil show pony for your amusment" laugh like your joking, or "i dont play for just anyone... are you just one of them normal, average girls, or have you actually got something unique about yourself that makes me want to play for you..." make her validate herself for you, obviously there are numerous ways you can say this and make her validate herself for you, theres just two examples, im sure you and everyone else on this forum can think of your own, but the point is make it something just out of reach... cat string theory with your guitar... make her keep validating herself, but with each validation move with the topic and create a conversation out of it, so it doesnt seem like an interview.

I always play guitar at dorm parties and I've played a few house parties too. It's a great way to chill and be the focus of everyone for a short time... and you only have that short time to make an impression. So here is my analysis:

Problem: People will lose attention and you need to find a way to keep it. Especially your target's attention.

Solution: If I am at a dorm party where I know most of the people and maybe a few randoms are there, I will play a song everyone knows, but I will change the lyrics to include the target's name. For example I may play Mr. Jones by Counting Crows which everyone will sing and then instead of singing "Cut up, Maria. Show me some of them Spanish dances..." I will replace "Maria" with my target's name. Usually people will laugh a little and it just makes an overall good vibe.

Another fun thing to do when you are playing for people is to just strum chords and make up funny lyrics as you go. I would gear each verse to pick on another person in the room - keeping it light hearted obviously.

One problem I've run into is that closer friends or the party regulars are a lot less interested in the playing than the newbies and people I see less often. Do you not play as much at parties where there are a bunch of regulars?

Right, I would tend to play more songs if the crowd is made up of randoms because they haven't heard you play before so their attention will be more focused on you. You have the chance to expose your personality through the songs you play and use humorous add-ins to make an impression on them.

When playing for friends and regulars, they have heard you play before so there is less of a need for them to pay attention because it is all repeat in their minds. You just need to find new ways to catch their attention while in this case. Ex: throw their names into songs, impromptu chords and lyrics, or ask one of the girls to accompany you in singing so the performance is different.

I tried making stuff up and adding people's names to the song at a party last night. Everyone was really digging it and laughing. It's all about being creative and getting the flow of the music going.