being new to the hobby I'm curious what it means to party friendly.  Arn't all get togethers a party?  Also I know what 420 is but when providers say they are 420 friendly?  

usually cocaine or crack cocaine.

As you can imagine, 420 friendly means that they like to smoke pot during a session.

Unless the drug is legal in your state, I would steer clear of people who advertise themselves as drug friendly.  It is often a way of LE getting a two for one bust.