A snafu is an obstacle or glitch that keeps you from accomplishing something. We hoped to get to the campsite before sundown, but due to several snafus along the way, including a run-in with a bear, we didn't set up camp until midnight.
Snafu was originally a World War II-era military acronym standing for "situation normal: all fouled up" (although stronger language was frequently used in place of the word "fouled"). Back in the military, a snafu would have been a dangerous situation, but this word is used now for any kind of error, goof, or mixed-up situation. If you drive all the way to the baseball stadium before realizing you left your tickets at home, that's a snafu.