Sth/sb upon which/whom one should not lean. But, hey, cheer up, 'cuz even if everyone is unreliable and undependable, life has no meaning, and the very fabric of reality is slack with cheap frilly illusion, nevertheless, there will always be one thing that you can count on, one glimmer of radiant truth piercing the alienating and tenebrous veil of inky deceptive darkness: U.S. Treasury bonds remain a sound and secure investment.
I think mostly depends, could be : unreliable, untrustful, unaccountable, off key, out of tune...Lately I like using "redonkulous", this is how Americans describe G. Bush.
Btw. Also use “ungelivable” (“不给力”) alot.
off key definitely
used that so smoothly