According to the The Hitchhiker's Guide to the Galaxy, Vogon poetry is the third worst in the Universe.
The second worst is that of the Azgoths of Kria, and the worst is by Paula Nancy Millstone Jennings of Sussex, who perished along with her poetry during the destruction of Earth, ironically caused by the Vogons themselves.
Fun fact: in the original radio-series version of HHGttG the name was "Paul Neil Milne Johnstone" and allegedly he was an actual person known to Douglas Adams, who was Not Amused at being used in this way, hence the name-change in the books.
(I do not know whether said actual person actually wrote poetry or whether it was anywhere near as bad as implied. Online sources commonly claim that he did and it was, but that seems like the sort of thing that people might write without actually knowing it to be true.)
[EDITED to add:] Actually, some of those online sources do in fact give what looks like good reason to believe that he did write actual poetry and to suspect it wasn't all that bad. I haven't so far found anything that seems credibly an actual poem written by Johnstone. There is something on-screen at the appropriate point in the TV series, but it seems very unlikely that it is a real poem written by Paul Johnstone. There's a Wikipedia talk page for Johnstone (even though no longer an actual article) which quotes what purport to be two lines from one of his poems, on which the on-screen Terrible Poetry may be loosely based. It doesn't seem obviously very bad poetry, but it's hard to tell from so small a sample.
The second worst is that of the Azgoths of Kria, and the worst is by Paula Nancy Millstone Jennings of Sussex, who perished along with her poetry during the destruction of Earth, ironically caused by the Vogons themselves.
Vogon poetry is seen as mild by comparison.