This expression came from the H-game (PC)/PS2/DC/anime Kanon. Ayu Tsukimiya's line (and probably the most famous throughout Kanon). This is her expression when she moans, or whines (like eeeehh, but more original).

Darn though. She had a sad story. One of my few favorites besides Nayuki.
Ayu: I'm cooking cookies.
Yuuichi: I bet they'll taste terrible.
Ayu: Uguu! I've learned how to bake from Akiko-san!
Yuuichi: You can't learn how to bake with just watching in a day..

..although I'll eat them if you manage to make them look good.
Ayu: Really?! Then I'll do my best!
by Welp June 15, 2004
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"Damn...it's coming...UGUUUUUUUU!!!"
by Peachie November 19, 2007
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"oh my" but sexy like
You got a message from tom online;
uguu, it seems naughty!
by PharaohofDuels December 9, 2022
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