MISTAKE #1: Using it in formal situations. This is the most critical rule. Never, ever use 屌 with a teacher, a boss, an elder, or in any professional or academic setting. It is strictly informal slang. Using it improperly will make you sound incredibly rude and uneducated. Stick to words like
厉害 (lìhai) or
很棒 (hěn bàng) in formal contexts.