Underwear stuffing is the act of placing the majority or entirety of a pair of underwear into a character's orifice, such as the mouth, vagina, or anus.

Notes

• Underwear in mouth, underwear in pussy does not necessarily denote underwear stuffing (e.g. holding between teeth, cameltoes)
• Through underwear does not constitute the tag, as only a small portion of the fabric is inside the character.

See also:

• panty stuffing - specifically for feminine underwear
• underwear gag - specifically for underwear stuffed into one's mouth, but not necessarily down the throat
• clothing inside - insertion of various articles of clothing, non-specific to underwear
• clothing in pussy - clothing inserted inside a character's vagina
• clothing in anus - clothing inserted inside a character's anus