Occasionally when I shower I get this vivid vision: a man comes home from hard days work and takes a shower. Grabs his shampoo but only squirts out half of his usual amount because shampoo bottle is empty, he thinks it will be enough but after applying it instantly feels it's not enough, so he grabs his wife's shampoo, squirts the second half and rubs it onto his hair. Few seconds later his hair bursts into fire because different chemicals in two completely different shampoos reacted together. How plausible is this scenario?