Reply to 18mo mad and aggressive

Sorry i meant to put behavioral problems with children.. lol . I am new to this site so bare with me. My son is 19 months old and he is over all a really happy baby.. but sometimes he gets this mean mug poker player face. Usually when someone is trying to talk to him that he doesnt know or someone trying to talk to me that i don't know.. barely know etc.. I think he feeds off my vibe changes. He will just stare down someone..