I love every class, but right now I'm playing a lot of scout. His taunts are cocky and made of pure awesomeness. I hate people who act like that in real life, but in TF2 it just fits.
Scout: [after killing an Engineer] Here's something you shoulda built: a not dyin' machine.
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Scout: [after killing a Heavy] I am owning you, you fat bald bastard!
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Scout: [after killing a Heavy] $400,000 to fire that gun huh? Yeah money well spent
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Scout: [after killing a Medic] Ooooh your gun shoots medicine! That's intimidating...
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Scout: [after killing a Sniper] You'll never hit me! You'll never hit my tiny head! It's so tiny! I got a freakin, such a tiny little head!
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Scout: If you order now, I'll throw in a second beatin' absolutely free
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Scout: [after killing a Demoman] Depth perception pal, look into it!