うらめしや～！
Literally: "I hate you!" or "I envy your life!" A phrase often said by youkai, such as ghosts or possessed objects (like the Karakasa Obake), to express envy towards humans, whose place in the Six Realms of Buddhist belief affords them less suffering. It's an old phrasing not commonly used in modern Japanese and as a result it's often translated as "Boo!"
Tatara Kogasa of Touhou Project used the phrase in her first appearance in Undefined Fantastic Object and often uses it in fan works.
This tag should only be used when a character can be seen saying the phrase.