Alternative form of what has been seen cannot be unseen

(dialectal, especially African-American Vernacular) simple past tense and past participle of see

(Internet slang) The situation in which a chat partner in an online chat or email exchange or mobile text messaging exchange sees or reads the last message or email sent to them, but does not reply.

(Internet slang, transitive) To not reply after seeing or reading the last message or email that someone has sent them.