a. The amount of utility you derive from Nike is higher than the amount of utility you derive from Reebok. That utility might be due to a better more lasting shoe, design, or from such a things as the utility attached to wearing a brand that has created value around itself (ie. if it is cool to wear Nikes).
b. Upon examination I determined that the difference in prices and quality as well as my opportunity costs for other products for that last price difference, make it better for me to buy a Malibu. For example, say the extra $2000 have too high an opportunity costs that overweight your benefit from having the boxer over the Malibu.
c. This is because consumers' choice is multi-time and so that today you might have to have the money to go away for a week, but the utility derived from that money must be calculated in relation to future periods where you could spend the money. You might have all that money but if in the next period you won't be able to eat, naturally the utility derived from eating in the second period is higher than the utility from going to Mexico.
d. You like both ice cream flavors the same, same utility,.... the only thing left is to flip a coin.