Seeing incredibly ugly and depressing public art will never fail to enrage me.
Also, when people claim that ugly art isn't actually bad if it was done by someone who's proven themselves capable of creating "good" art. I've heard this argument used to defend countless works, most notably those of Picasso.
Just because Picasso painted beautiful things like this:
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...doesn't make things like this any less repulsive:
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You don't need an art education to recognize aesthetically unappealing art. People have no problem shitting on otherwise great musicians (including their favourites) when they release a terrible song, so why is this any different?