Cockblocking means: The act or attempt of impeding another's intended goal of a romantic relationship or sexual intercourse.. It is informal slang, fine in casual speech but not suited to formal contexts. It carries sexual or vulgar connotations; not alarming on its own but worth understanding the context your teen heard it in. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.