i think by fun he means being able to smoke the pants off other cars when he steps on it.
i say go get a muscle car! who cares what other people think. when they give you a dirty look rev the engine its how its works! lol im kidding
anyone can buy a fast car but not anyone can build one.
heres an idea that id love to do someday: pick up a cheap s-10 drop a 350 in it (or LS1, get the fun of fuel injection) and have fun driving that thing! find a 6 speed manual or 5 speed and then fun has a whole new meaning. and if its properly tuned and add a few MPG saving things on it you could see mid 20's MPG with it since its a light truck with a boatload of power...its a good sleeper truck.
Probably something with VTEC -- efficiency in the lower RPMs, and you hit the more aggressive cam on those rare occasions -- you still want to save gas, right?
Choices I'd pick in the "fun" and potentially efficient category from Honda:
Civic HX -- 96+ (efficiency-built)
Civic Si ('99-'00) -- I had one new and loved it
TSX -- currently own one and get 30 with mild hypermiling (wife drives it 90% of the time) -- used 06's go for around $25K
Civic Si (02+)
Mazda 3 (great handling -- 2.3L is more of guzzler than the 2.0L)
Mini Cooper (no need for the supercharger -- fun out of the box)
Impreza 2.5RS (essentially a non-turbo WRX)
You can hypermile anything, but as you can see, some have more potential.
the new Mini coopers are suposed to get close to 40mpg right? and from talking to people who have driven them they sound like fun, my brothers toyota celica alwas got 38-42mpg, and still is around some place with 340,000 miles or something crazy like that on it, and altho it was a little small inside for me, wasn't to bad to drive, handled great at 115mph too.
with $25,000 to spend on a car, the limits are almost endless when it comes to good mileage.