Can a cigarette set a formula 1 car on fire?

If you did it on exposed parts like say on the fuel then yes but it shouldn't if you just drop it on the body work. Carbon fibre is flammable but would only ignite and burn thoroughly when exposed to a naked flame i.e. a lighter. Look at times even as recent as practice of the 2014 Brazil GP. One of the Ferrari caught on fire but didn't burn the entire car down.