[evincarofautumn]

“Unf” is quite widely used as a spelling of a moan, to express sexual desire or gratification. While it can be used to express non-sexual enjoyment, the sexual connotation it evokes is just unnecessary when it comes to a programming language, regardless of the original intent.

[a_c_s]

While I've never seen this use personally, UrbanDictionary very strongly corroborates this.

http://www.urbandictionary.com/define.php?term=unf

[evincarofautumn]

It’s worth noting that “universal noise of fucking” is a backronym—the word was originally onomatopoeic.

[TazeTSchnitzel]

It is, still, but urbandictionary users like making inaccurate definitions as an attempt at "humour"

[david-given]

As an counter datapoint, this is the first time I have ever heard of this.

[TazeTSchnitzel]

Perhaps as "umph" or "umf"? No?

[david-given]

No, not even slightly.

FWIW, I grew up in Scotland, then moved to England, so I'm probably from a rather different cultural background than the poster.

[iagooar]

As a non-native speaker, I have seen "umph" before.