Co-workers hassling me about a girl..

Just start agreeing with everything they say and then take it to the next level of sarcasm. If they say something like, "Are you going to pick that girl up and take her on another "ride"?" Say, "Yeah sure. I'm going to do more than take her on a ride. I'm going to wear that out." Or something similar.
The reason these women are teasing you so much is because they are getting a reaction out of you. Remember in grade school? The reason people tease is they want to get a rise out of you. If you don't give them that rise the teasing will dissipate and probably end all together. Do it in a way you feel comfortable but make it into a joke and they will no longer find it funny.
Ignoring the problem will only make it worse. They still know it tweaks you and will keep on.

Ignore it. If it bothers you then just tell them that you really don't appreciate them talking about your personal life. Also tell them that while it's none of their business there is nothing going on. You felt bad for the girl and decided to give her a ride. Tell them you would have felt bad if you had just ignored her and then something happened to her. So what if you're a nice guy. Also suggest that they must have pretty boring lives to butt into your business. I know what it's like having coworkers tease you about something. In my case I liked my 20 year old boss and they'd tease me all the time about it. But I didn't let it bother me, I just went with it and joked around, I was sarcastic. It'll all blow over soon anyway. Maybe give them a taste of their own medicine sometime, that'll make 'em shut up. Hope this is helpful. (BTW my sitch went on for 2 years, so don't worry. you don't even work with the girl. they'll soon forget)

If they're older women, then all that they're going to do is gossip. They have nothing better to do and they're going to focus on it for a while. Just because they think it's interesting, and they have no lives. So,just ignore it and do not react when they say something, because it will only make it worse.

just ignore it, they just need something to talk about.
if you let it go, then they will too.

Aw honey, I'm sorry that your boss is giving you a hard time! ;[
You sound like an amazing gentleman. That was ONLY trying to help someone in need.
So you don't want to lose your job, well you will obviously feel weird about it, everyone would! :D But give it time, your boss will forgive and forget, and it will all be a figment of the past. It may take time for you to get over it, but I'm sure you will. It was just a kind thing of you!

I wish you soo much luck with your boss! <33 :D

Why be bothered or uncomfortable over this? If it was just a ride home for a stranded person then leave it at that. You don't have to explain to them and who cares what they think.