Is it normal that my coworkers refuse to accept i'm not who they thought i was?

The first day of training I made a big mistake. I was friendly toward a quirky, mischievous, class-clown type who I was paired up with and we became work "buddies". Immature types tend to gravitate toward me based on looks alone. I know it doesn't help my case, but my hairstyle doesn't scream serious academic.

At first, it was great making friends with someone who was so different than myself. I learned a lot and he made me laugh constantly. However, I soon realized that this guy was notorious with a lot of our coworkers. He had a "naugty" reputation, and because we hit it off so well, people had assumed I must be JUST like him. They treated me very differently than I'm used to being treated.

They figured everything out of my mouth was a joke or sarcasm and that I must always have my mind in the gutter when I make an honest borderline Freudian slip. They dubbed the two of us "the boys". I think everyone must assume I'm around his age (18), though I'm actually 25.

Any minor mishap was instantly blamed on us and everybody assumed I was an irresponsible slacker from the get-go, even though I'd done nothing to give them that impression. If I laughed, somebody always took offense as if I must be laughing at their expense. My boss doesn't take me seriously to this day and acts as if I'm some hooligan she regrets hiring, despite the fact I have a perfect employment record.

I admit that it was refreshingly exhilarating to be thought of as a "bad boy" at first, but now that any attempt I've made at exhibiting my true nature has been dismissed as a joke, I'm beginning to feel frustrated. This is turning into a kind of identity crisis, but an external one! I feel like I'm in a lame comedy film. I was the serious nerd who became associated with the "wrong" crowd and ends up roped into their trouble.

This siutation transversed annoying and ended up smack dab in the middle of outrageous ever since my colleagues have taken to the idea that I'm flirting with one of my female coworkers. Everything out of my mouth in front of her is taken as innuendo. I feel so sleazy, as it's not my intention at all. The worst part is I think this girl really is kind of freaked out by me! I don't even like her. This whole thing is an insult to my intelligence and perilous to my employment and reputation.

Though I'd love to know if this is normal, any advice you can offer will be very well received, as I really can't seem to convince anyone, despite evidence presented, that I am who I say I really am. Help!