In the UK, the Highway Code is clear that the horn may be used only to alert another driver of your presence. It is preferable to flash your lights, especially

In the UK, the Highway Code is clear that the horn may be used only to alert another driver of your presence. It is preferable to flash your lights, especially late at night. It is not permissible to use the horn to celebrate a sports victory, to signal sympathy with a striker's picket, to demand that another driver get out of your way, or for any other purpose than to signal your presence. The Highway Code isn't law, but you are required to be familiar with it to get a driving licence, and failure to comply will predispose courts to find you guilty if you are charged with harrassment, obstruction, intimidation and so on. Dunno how it works in Canada.