There is a mitzvah of simchas yom tov with basar. If you want to be makayeim milchigs, have that in beginning of the meal, then (after the cheesecake mid-meal dessert) change over to fleishigs, bring out a 2nd challa l’zecher the shtei halechem, and then have meat.
(I am well aware that many people have exclusively dairy meals on shavuos. This is especially helpful if you want to have milk with your coffee. I’m just being weird in an attempt to post a 147-like post)