Airhorns were used for emergency signalling at the camp I went to as a child and then later worked at, so not only do they startle me in the usual way they activate my fight-or-flight response.
As a counsellor, three blasts on an airhorn meant we needed to do a water search. This meant running down to the lake while shedding clothes, ready to dive in immediately. If you want to see me rip my shirt off at high speed and go for a swim in my scanties, all you need to do is set off an airhorn near a body of water.
That wouldn’t have been Ontario Pioneer Camp, would it?
Nope, YWCA Tapawingo. I think it’s pretty common though! At any large event at which airhorns may be heard I can usually spot a couple of other twitchy ex-camp-counsellors whose hands keep going to their shirts whenever the airhorns go off.