I recently stumbled upon a page that said this:
Eating Dairy Products on Shavuot
Many families have a custom to eat dairy products on Shavuot. As noted above, Darkei Teshuva questions this minhag based on the obligation to eat meat on Yom Tov. Darkei Teshuva's assertion is based on a number of assumptions. First, nowadays one can only fulfill the mitzvah of simchat Yom Tov by eating meat. Second, the mitzvah to eat meat is obligatory. Third, the mitzvah of simchat Yom Tov applies to every Yom Tov meal. Fourth, there is an obligation to eat meat on the first night of Yom Tov, and therefore, eating dairy products the first night is not an option. Those who eat dairy products on Shavuot reject one (or more) of his four assumptions.
I had never heard that milchigs were forbidden on any Yom Tov, let alone Shavuos.
- Has anyone else ever heard of these minhagim?
- How common are they? Which groups observe them?
- How severe is the prohibition considered -- or is it more of a coincidence? (That is, for example, if one were allowed to eat before kiddush, would it be OK to have some milchigs for breakfast?) Is the prohibition against eating milchigs per se -- or against, as it were, not eating meat?
- Do the same people consider milchigs an assur for Shabbos, too?
Related: Waiting Less Time on Shavuos
I recently talked to someone who accepts all four assumptions in the quote in the question, and eats both dairy and meat at every meal of Shavuos. He does so by eating dairy first, making a break in the meal (=eating pareve courses and possibly washing his mouth), and then eating meat.