Fail is a pretty popular term on the internet these days, and one I'm quite fond of.
Looking in my Chinese dictionary I can't find a great equivalent - is there a good way to say this? What would be the best word to use?
Direct translation of fail would be 失败
However, in internet context, I think 糗(qiǔ) is more suitable.
糗 means embarrassing, usually as a result of you failed something...
When used as verb, you would say 出糗, means you did something embarrassing. For example:
囧(jiong3) to fail，or 囧大了，囧大发了 to epic fail
When fail use to describe some fails in movie/tv drama, we say 穿帮
I would suggest "悲剧" (mainland China).
"悲剧" literally means "tragedy". When you "fail" to do something, it's really a tragedy (haha).
This usage gained popularity in recent years among mainland Chinese Internet users.
I think "悲剧" is a better translation of "fail" compared with "囧". I use "囧" when I'm embarrassed or frustrated, similar to "呃" and "无语". "囧" as a slang has the same meaning as "窘" in "窘迫" (uneasy).