What trouble can I face at a house party with alcohol and possible weed?

Ok so I live in Massachusetts where the marijuana law is decriminalized to an ounce or less is a fine. My question is if I go to a house party at a friend's house (not my own) and smoke/drink but don't have any weed on me and drink very little, can I get in trouble for anything if police are called? There will be 1 possible minor at the party, and I know the host is responsible in this state, however, is everyone else (including me) at the party responsible as well? I have a designated driver and don't plan on getting smashed since the party consists of co-workers, I just want to know my rights as the party go-er not the host or the underage kid or the one with possession of pot. Just the party go-er who partakes.