You're friend who you talk to all day on Sundays, and no one else. they are irreplacable. the only time you can have a different sunday buddy is when they are not home or if they die. And there are rules to Sunday Buddies:
1: You have to know them
2: You have to get along with them
3: It has to be someone no one would think of.
4: Has to be able to talk about something all the time (no awkward moments)
5: has to have a brain that works the same way as you, but uses it differently
"hey dude, wanna be my Sunday Buddy"
"sorry I already have one, you can be my backup one if you want"