Very good posts. If it's one of my *best* friends, it's off limits. Any girl they've been serious about = no way. Now, we've shared girls that were just "fun girls" if you know what I mean. Sex and actual emotional attachment are two related but separate issues.
In case it wasn't otherwise answered, "snogging" is what is sometimes called "flinging." It comes between kissing and shagging.
Second and Third base in Meatloaf terminology.