"Blow one's own trumpet" (or "horn") is an idiom meaning to brag, boast, or talk proudly about one's own achievements, skills, or successes. It often implies excessive pride or arrogance, though it can sometimes refer to necessary self-promotion.
It originates from the medieval practice of heralds blowing trumpets to announce a king's arrival, suggesting that a self-boaster is acting as their own herald. It also likely relates to biblical warnings against announcing charity with trumpets.
Abraham Fleming, a 16th century English philosopher and writer, used the phrase in his first major publication: "I will sound the trumpet of mine own merits." Sometimes expressed as "tooting your own horn".
From online with editing
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There were a couple funny posts and discussions about "吹牛" and "夸张" in 笑坛 recently, which reminds me of this idiom. Just "吹牛" means to knowingly twist the facts and tell outrageous lies, which is more than bragging or boasting.
We all have an ego and there's nothing wrong with being proud and self-promotion when necessary, as long as the pride is on solid ground. But "吹牛" is a big no-no IMHO: the person doing so may become a laughing stock when being found out. 
And, there are professions which seem to like "blowing one's own trumpet" （and“吹牛”）more than others, with politicians at the top of the list. 
That's it for this rainy Tuesday.
