Short pants are generally not allowed in public places (hospitals, etc.). When visiting monasteries and cathedrals, dress modestly.
Taking off the lower half of a swimsuit on a beach would certainly cause a fuss and is usually reserved for authorized nudist beaches.
When toasting and clutching glasses, you must look the opposite person in the eyes; otherwise, it is considered disrespectful.
In Montenegro, being obviously intoxicated is a sign of poor taste and character: you may be asked to drink gallons, but you are supposed to be able to handle your drink. People also like to sip their booze rather than dumping it “bottoms-up.” Beware: “rakija,” a plum spirit with a high alcohol level (typically about 53%), is stronger than anticipated and can get you drunk quickly!