A person who promises never to do drugs, drink, smoke, or have promiscuous sex. They may also abstain from other "taboo" things. However, the name of straightedge is being tarnished by people who act "high and mighty" and think they are better than other people just because they say it.
Ruins the name:
'Hey, I'm a straightedge, I'll NEVER do drugs or drink or smoke like any of you.'
'whoop dee fucking doo, we totally give a shit, and we totally think you're way better than us </sarcasm>'
A good straightedge:
'Hey, wanna go out for a drink and stuff tonight?'
*at the bar*
'I'll have a nice, cold beer'
'I'll just have a coke'
'oh, I forgot to mention, I'm what you would call 'straightedge'
'OH, I totally respect that, at least you aren't shoving your beliefs up my ass!</sans-sarcasm>'