A person you can always depend on to help you in a really messed up situation where you need a quick excuse/escape.
This person will always have that six sense to
lie in favor of you when asked about your current location (sometimes
without you giving them any real hint about it).
This person also happens to be in the right place
at the right time when you're in trouble.
"Dude, that blind date is horrific! I need to call my
lifeline."
Or...
"Thanks, man! You're a lifeline!"
In situations where you're
running late getting into work:
Boss: "Do you know if your name came into work today?"
Lifeline: "
Uh... Yeah, he came in an hour before I went on lunch break. He's somewhere around here."