Task: Determine the prevailing emotional tone of the tweet, categorizing it as either 'neutral or no emotion' or as one or more of the given emotions (anger, anticipation, disgust, fear, joy, love, optimism, pessimism, sadness, surprise, trust) that most accurately represent the tweeter's mental state.
Tweet: @Rocks_n_Ropes Can't believe how rude your cashier was today when I was returning an item!  Your customer service is slacking.
This tweet contains emotions: 
anger, disgust, sadness