小子 (xiǎo zi) is a colloquial noun for a young male, but its tone depends heavily on context. In a neutral or affectionate context, it means 'boy' or 'guy' (like calling someone 'kid'). In a derogatory context, it becomes an insult meaning 'joker' or 'despicable fellow'. It often appears in fixed expressions like 臭小子 (damn kid) or 傻小子 (silly boy). Be careful with the connotation — using it with strangers can be rude.