Oh, man!
Sounds like a bunch of teens "Uh, how fast does it go?!
What an ignorant question...
To those type of bold/prying/lame questions (esp if not from a fellow stanger), I'd answer with something like:
1) Is your car really fast? -- "Naah, it's really slow"
2) What does that car run at the dragstrip? -- "It runs 15s"
3) What's your top speed in it? -- 65
I'm not a bad guy, but ignorant or prying questions about my car from someone I've never seen b4 annoy me.