Same problem here! One roomie made banana bread which requires rotten bananas which started our fruit fly problem and the other juices which maintains it!

Easy peasy, just throw her fruit out after she leaves it on the counter.

Zip-lock bag. few coins. fill zip-lock bag half way up and hang from the ceiling over the door and the flies think it is a hive so they wont enter the house :)

Buy him a few containers for his fruits- problem solved.

Try putting a glass of red wine or vinegar on the side, with cling film on top and small holes poked in the cling film. The fruit flies will be gone in no time.

Place a few pieces of rotten fruit at the bottom of your beer bottle. Put a cone of paper on top, so it's a funnel to the fruit. It will trap all the fruit flies in there then you can throw the whole bottle of fruit and fruit flies out. Fruit attracts fruit flies. Bottles can kill them. :)

Is this in North Carolina? Because I had a roommate a few months back who is exactly like this. She had her own compost pile of rotting fruit and blamed me for the fruit flies.

Then why aren't YOU just throwing it out? Yeah your roommate is the one buying it, but you're also letting it sit there long enough to rot.

And people wonder why I live by myself.

Either way, apple vinegar in a saucer will fix the bug problem.