knock boots

"knock boots" is sexual slang. In short, it refers to to have sexual intercourse, especially recreationally if not casually. Among teens it is usually used jokingly, as crude banter, or in TikTok-style algospeak rather than as a serious statement of behaviour. Persistent or aggressive use directed at a specific person, especially online, is the bit worth paying attention to: that can shade into harassment. If you hear it once in a chat with friends, it is probably nothing. Repeated targeted use deserves a conversation about respect.

"knock boots" is informal English meaning to have sexual intercourse, especially recreationally if not casually. It is used widely across English varieties. A more formal or neutral equivalent would be something like "to have sexual intercourse" expressed in standard vocabulary. A common mistake is to assume "knock boots" can replace its standard equivalent in every register; keep it for spoken or casual situations and use the formal form in writing. If you are a B2 or C1 learner, it is useful to recognise this word when you hear or read it, but think carefully about whether the situation really calls for it before using it yourself.