Xvito said:
Um... Crimes can't be victimless... That's why crimes are crimes, because there are victims...
"Victimless crime" refers to an act that's illegal and therefore a crime, but doesn't involve a victim. Like, for example, smoking a joint. Pretty simple.
And to answer the question, no, I wouldn't. I'm no rat. My friend would have do something genuinely terrible, like murder or rape someone, for me to consider snitching them out. Not only is squealing against my principles, there's also the old adage about snitches ending up in stitches to consider.