I like to think of them more as guidelines than rules. Something set, but negotiable.
The youngest of my teens to have a girlfriend was in eighth grade. He used to go to her house often to hang out, watch movies, whatever. Her parents and I had a lot of communication. I didn't see that him having a 'girlfriend' differed much than having a 'girl friend' KWIM? We live within walking distance of a movie theater, so they've all gone on group dates to the movies.
They aren't allowed to have girls in the house when I'm not home. As long as I'm home, they are allowed to have girls in their bedroom. I make excuses to bring clean laundry in or whatever periodically. Just enough for them to know that I could interrupt at anytime, lol.
Of course they aren't ALLOWED to have sex, but when has that ever stopped a teenager? They know my feelings on the subject, but they also know how to protect themselves.
I say no smoking, no drinking, period, because it's illegal at this age. Drugs are always illegal. Not my rule, the entire country's rule.
All three of my teens wanted their ear pierced when they were like 7. I told them when they were teenagers. One out the three still wanted it done. He got his ear pierced at 14. Recently, after much discussion, he got his eyebrow done too. Tattoos they must be 18.
Hair color I wouldn't object too. Same with clothes and stuff. Hasn't been an issue yet.
They have a curfew of 9:30 on weeknights and 11:00 on weekends, but it is negotiable if there's a good reason.
That's about all I can think of right now!