In Patrick Suskind's novel, Perfume: The Story of a Murderer, the first irony I see is that the book's title refers to perfume, but the first several paragraphs of the novel describe the different kinds of "stenches" that weave about the bodies, the market place, the homes, and "businesses" of that time: of slaughter houses, dirty bodies, rotting teeth, and chamber pots, etc. The irony is that with the title, one would expect to start reading about something sweet smelling, rather than so many nasty elements of the society of the time.
I also find it ironic that when the smell of the dead and rotting corpses became unbearable because cave pits had fallen in, that when the people complained, the Cimetiere des Innocents was "closed and abandoned," but on top of all this death, the businesses of the living were placed on top.
Millions of bones and skulls were shoveled into the catacombs on Montmartre and in its place a food market was erected.
If anything, I might expect that a slaughter house or some kind of mill might have been built in its place, but not anything to do with eating and healthy people.
Another form of irony is found in the description of Grenouille's mother on the day she gives birth to her son. The speaker tells us several things that seem to portray this young woman as if she is still appealing, but the details are rather nasty, even though they are presented as "positive features."
Grenouille's mother, who was still a young woman, barely in her mid-twenties, and who still was quite pretty and had almost all her teeth in her mouth and some hair on her head and—except for gout and syphilis and a touch of consumption—suffered from no serious disease, who still hope to live a while yet, perhaps a good five or ten years...
There seems a great deal of irony here. Perhaps it is found in that the norms of that era are very different as opposed to the norms of present-day society—but the idea that she has "no serious illness" (while having gout, syphilis, and "a touch of consumption") all seem like severe diseases. The concept that the baby's mother assumes that in her mid-twenties she will have lived a good life if she lived beyond the next five or ten years seems ironic in a modern context. If the mood or the tone were different, I would expect that these last elements would simply seem like historical norms, but in the way they are described, along with so many other unappealing aspects of the time, the images sound ironic instead.