so what is the spies nemesis, i get killed frequently by spies when i'm a heavy, medic, engy or sniper, all of which are vunerable to spies due to the nature of those classes, is the problem with the spy down to the fact that it has an impact on too many things, such as an uber counter and sapper and disguise and cloak and dead ringer.
Like me, you're probably not playing in the right mindset for spy. Watch the masters and you'll probably see that they move and attack in completely different ways to people like me. Heavies use cover and time their movements, they also get bogged down in firefights and this is alien to spies.
Well neither demo nor solly have a direct nemesis.
Pyros are nasty work for demo men on some maps. I admit that spammy maps are good enough on defence, but once a pyro runs at close range you're literally toasted.
As for soldiers, I get taken down (when I play heavy) by Ringel, Claws, Cheez, Dodgy Emu and Brahms. Soldier has the advantage of range if he uses it wisely. The best soldiers pop in and out of cover to attack the heavy, who can't really afford to do the same thing at close range.
For my opinion on how "nemesis" classes stack up:
Engineer - more vulnerable to demo man or spy
Spy - more vulnerable to pyro (especially after dead ringer)
Heavy - more vulnerable to spy and sniper
Scout - more vulnerable to heavy, pyro and sentry guns
Medic - vulnerable to all classes IMHO (but trades vulnerability for uber charge benefits and team longevity)
Demo - more vulnerable to pyro and spy, soldiers and other demo men
Soldier - more vulnerable to sniper, spy and engineer
Sniper - more vulnerable to spy and other snipers, demo men on some maps
Pyro - more vulnerable to soldiers and heavies, sentry guns and of course, other pyros