go on about
phrasal verb.to talk about something for a long time in a way that is boring or annoying for other people.
phrasal verb.to speak at length and repetitively about a specific topic, typically to the annoyance of the listener; functions as an intransitive or transitive verb with 'about'.
“He always goes on about his expensive new car.”
“I wish she would stop going on about her ex-boyfriend every time we meet for coffee.”
“The lecturer went on about the importance of primary sources for nearly an hour, leaving little time for the actual seminar discussion.”
usually used in a negative way to describe someone who talks too much about one topic.
this is a great phrase for teaching the 'annoyance' function of the present continuous, as in 'He's always going on about...'
the preposition 'about' must be followed by a noun or a gerund, not a 'that' clause.