noun
wearing only underpants
Slang abbreviation of パンツ一丁. Used for someone wearing nothing but underpants, often in casual or humorous contexts.
See also: パンツ一丁
朝起きたら弟がパン一でリビングにいた。
When I woke up, my younger brother was in the living room wearing only his underpants.
夏は暑いから家ではパン一で過ごすこと
In summer it's hot, so I often hang around the house in just my underpants.
Abbreviation of パンツ一丁 (pantsu itchō), literally 'one pair of underpants'.