The tag implication #53454 diaper -> underwear has been rejected.
Reason: At first there was topic #27468 (diaper -> underwear). It was rejected.
Then there was topic #27743 (diaper -> clothing). It was rejected.
I'm with the people in both threads who point out that diapers are usually worn under clothing, clothing is never worn under diapers, some diapers are deliberately designed to resemble underwear to the extent that telling them apart under TWYS may be difficult in some circumstances, and it is in fact possible for an article of clothing to serve a functional purpose without losing its designation as "clothing".
EDIT: The tag implication diaper -> underwear (forum #386910) has been approved by @slyroon.
Updated by auto moderator