Ex-Queens of the Stone Age Guy -- I'm No Cop-Thwarting Gun-Toting Druggie

Former Queens of the Stone Age bassist Nick Oliveri insists he wasn't packing heat OR drugs during a tense standoff with a S.W.A.T. team in L.A. last summer -- pleading "not guilty" today to all five charges stemming from the incident.

TMZ broke the story ... Nick was arrested last July -- after a fight with his girlfriend escalated into a four-hour standoff with police. Oliveri was booked on felony domestic violence -- and after police searched his home, they say they found a fully-loaded rifle.

According to the charging docs, police also found cocaine and methamphetamines during the search.

Oliveri was charged in August with two counts of possession of a controlled substance with a firearm, 2 counts of possession of a controlled substance, and one misdemeanor count of resisting, obstructing or delaying a peace officer.