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2.
A toilet seat used for sleding.
Jimmy, grab your awesome butt coaster. its snowing!
by kyle bingham August 13, 2008
 
1.
A towel, or other absorbent material, used to protect a bed, bench, chair, etc., from the residue moisture left over on one's posterior after a shower, bath, or swim. The towel acts much like a coaster that is used to protect furniture, except this time it's protecting the bed from your wet butt.
"Can't you please use a butt coaster" said Jean, after I got our bed wet by sitting directly on it after coming out of the shower.
by Poor David October 13, 2013