A friend who is only a friend when circumstances are pleasant or profitable. At the first sign of trouble, these capricious, disloyal friends will drop their relationship with you.

A friend who is only around when they need you.

A friend who is only nice to you when it's convenient. Someone who's wishy-washy. Someone who is a "backstabber." Someone who abandons you in certain situations.

a friend who only sticks by you when things are going well.

A friend who doesn't help in times of difficulty. Likely nautical in nature, referring to the fact that when weather is good nearly anyone can help on a ship.

A person that is a brilliant friend while things are going well, but when the gong gets tough, the person ups and leaves.

a psuedo friend. One who pretneds to be your friend when things are good. Leaves when things go astray or are not quite like they think they should be.