Here in Canada where motorists don't even acknowledge motorcycles (let alone respect them) I need something more assertive. When a SUV-driving soccer-mom casually invades my space I want to let her know that "Here I am!" and "you fucked up!" A loud horn blast accompanied with a scolding stare or rude gesture should do the trick.
I bought a truck horn at Canadian Tire that claimed to have a "big rig sound".
The old horn next to the new one:
The new horn is bulkier but fit easily without any steering or suspension clearance issues. If I were to panic-brake HARD and fully compress the fork, the fender might touch the horn but it won't do any damage.
New horn installed:
"Before" video with polite little Japanese horn:
"After" video with new loud horn: