Wikipedia
Risk-seeking
In economics and finance, a risk-seeker or risk-lover is a person who has a preference for risk. While most investors are considered risk averse, one could view casino-goers as risk-seeking. If offered either $50 or a 50% each chance of either $100 or nothing, a risk-seeking person would prefer the gamble even though the gamble and the sure thing have the same expected value.
Risk-seeking behavior can be observed in the negative domain x < 0 for prospect theory value functions, where the functions are convex for x < 0 but concave for x > 0.