In other words, to pull off a successful boast, you need it to be appropriate to the conversation. If your friend, colleague, or date raises the topic, you can go ahead and pull a relevant boast in safety. Alternatively, if you’re forced to turn the conversation onto the required topic then you must succeed in provoking a question from your conversation partner. If there’s no question and you raised the topic then any boast you make will leave you looking like a big-head.
It makes perfect sense. First of all, purely in terms of how much I impress you, an unprovoked boast is almost completely ineffective. Because everybody in the world has something to boast about. If I get to pick the topic then I will pick that one. If you pick the topic or ask the question then the odds you serve me a boasting opportunity are long unless I am truly impressive on many dimensions.
And it follows from that why you think I am a jerk for blowing my own horn. I reveal either that I don’t understand the logic and I am just trying to impress you or I think that you don’t understand it and I can fool you into being impressed by me.