Someone was making fun of me for my idiosyncratic habit of using generic placeholder names in my everyday speech. When I thought about, I realized that I use a lot of them.
Aulus Agerius and Nomen Nescio (The classics)
J. Random Friar, J. Random Nun, J. Random Catholic, J. Random catechumen, catechu-kid, etc. (This is a riff on a hilarious intercession once reported to me, in which the assembly prayed for the catechumen and catechuwomen.) Joe and Jane Daily Communicant, Joe and Jane Frequent Penitent, etc. (J. Random is a convention in computer slang.)
Shlomo ben Plomo and Plomo ben Shlomo, generic rabbinical authorities.