The Japanese title is Yahari Ore no Seishun Rabu Kome wa Machigatteiru with subtitle My Youth Romantic Comedy is Wrong as Expected. The subtitle already pretty much translate the Japanese title. So, what is the SNAFU in its English name? How did it get there?
Here, the word for wrong - "machigatteiru" - is being changed into "snafu," which, according to the dictionary is "a badly confused or muddled situation"
When translating literally, we could just use "wrong" (as in the subtitle you mention). However, an important thing to note about anime is that translations are almost never exact. Whether it's just the dialogue, or the entire anime name, many things can be changed to suit a western audience.
For instance, consider the title "chuunibyou demo koi ga shitai" (Literally: Chuunibyou, but I want to do love) which in English is officially titled "Love, Chuunibyou, and Other Delusions." A much more marketable title.
Similarly, with Oregairu, the English licencing company likely decided that using a more "interesting" word like "snafu" would make the show more intriguing to western consumers, thus improving sales.
I suspect that whoever decided to use the "SNAFU" translation for the title was going for the original military acronym "Situation Normal, All Fucked Up", rather than the contemporary non-military meaning of "something that has gone wrong".
Why? Well, the title in Japanese is "yahari... machigatteru", which means "...wrong, as one would expect". If that isn't a borderline literal (if less vulgar) equivalent of "Situation Normal, All Fucked Up", I don't know what is.
(This is also, in my >opinion, a better translation choice than "...is wrong as expected", which is relatively unnatural and pretty obviously directly calqued from Japanese.)