I've never really enjoyed coke all that much. First 20-30mins are fantastic, but it's all downhill from there: Anxiety, paranoia, cravings, restlessness.
For some weird reason I keep coming back for more. It's readily available usually (for free, never spent a dime on that crap) and the comedown can be shaken off with some pot, benzos and/or booze. With each time doing it it becomes more of an issue. I catch myself thinking about it, seeking situations where it'll be available, like my brain is telling me it wants more without realizing it'll just make me feel like total crap. Like that stuff is reprogramming my brain. God I hate coke. :D
And about the doing it once or twice... That's exactly how pretty much everyone starts off. I've heard soooo many people tell me they could never become addicted cause it makes them feel like shit or is just inferior to so many other drugs. Most of em end up with coke as their drug of choice for years after I hear that.
The stuff is nogood I'm telling you and no good will come off it. ;P I have a feeling you're gonna do it anyway when you're in a drunk state and are offered a line. Just keep in mind, that your brain is enjoying it a lot more than it might be telling you at first.
Needless to say advice would still go something like this: Don't do it, the first line will start that reprogramming process for sure.