If you have bad luck, or somebody else has, you can use one of the following expressions. The one at the bottom is used for instance when somebody has missed a chance. It’s quite informal but very common!
Jammer, niets aan te doen
That’s too bad. Nothing we can do about it.
Dat is pech hebben!
What a pity!
Helaas, pindakaas!
(litt.: That’s too bad, peanut butter!)That’s just too bad!
Note: By the way, do you know you can actually buy Helaas Pindakaas? Visit www.helaas.com to see for yourself.