I opened the bottom window sprayed upward a bit, then lost my nerve and quickly closed the window. The wasps sprung to activity, perhaps they were stunned a little though, but I was feeling a bit emasculated because when I "lost my nerve and quickly closed the window" I let out a squeal of sorts. A high pitched yelp. And I had company.
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I wouldn't feel too bad about the yelp.
I'm pretty sure the prospect of being set upon by hornets would've inspired even Genghis Khan to let out a squeal or two. After all, when one stings, a pheromone is released alerting others to join the fray. It's always a packed party when Vespa Crabro's in the club.
Sounds like you settled on a good strategy. What product did you use?
.d.