If you blow your own trumpet, you are boasting about your achievements and abilities.
He's always blowing his own trumpet - it's so boring! Why can't he be more modest about his abilities?
You've got to blow your own trumpet a bit more, otherwise you won't get a decent job!
The phrase to blow your own horn can also be used in a similar way.
Clare finds it hard to blow her own horn because she's very shy.
An alpenhorn or alphorn is a long wooden horn. It was traditionally used by shepherds in Switzerland to call the cows from the pastures and into the barn at milking time and to communicate with other people across the Alpine mountain region. It is now played for fun as a musical instrument.