"40 mike-mike" describes any weapon firing a 40mm grenade. Heard in rap lyrics, drill music, video-game chat or street-style social media, it is more often quoted than acted on. What matters is context: are they repeating a song line, or are they describing specific people, places and plans? If the language pairs with secrecy, sudden new friends, or worry about someone they know, that is the cue for a calm direct conversation, ideally before involving anyone else.