Oh, man. I had a bad fruit fly problem once. I decided the solution was to fill a spray bottle with Isopropyl Alcohol and use a lighter as a miniature flame thrower. It was effective for the ones caught in the blast. I killed off another batch later when the counter and curtains caught on fire from the unspent fuel that landed on them.
The fumes were pretty bad... I'd forgotten how fast it would evaporate. Eventually I had to stop. Minimal singing to the counter & curtains (the wife was out, of course, and she hasn't noticed). Overall, it was rather satisfying.
That said, I later learned the little buggers actually use alcohol for their woes. So maybe not the best choice.