In just four lines, this tiny poem captures a very familiar kind of discomfort: being stuck at a work dinner you'd rather not be at. The oysters arrive, and the speaker gets sick, though the poem leaves it unclear whether the oysters themselves are to blame or whether the whole event has turned the speaker's stomach.
The clever part is the phrase "their dull company." It's odd to call oysters dull company, since they're food, not guests. But that slip suggests the speaker feels the same about the human colleagues around the table. The title, "Collegial," points the same way, since it means friendly and cooperative in a professional sense, and the poem quietly undercuts it. The short lines and the blunt, deadpan ending, "and I am ill," create a dry, wry mood. There's no drama, just a flat statement, which makes the awkwardness and queasiness feel funnier and more real.