trousers, 1840, see pantaloons. Colloquial singular pant is attested from 1893. To wear the pants "be the dominant member of a household" is first attested 1931. To do something by the seat of (one's) pants "by human instinct" is from 1942, originally of pilots, perhaps with some notion of being able to sense the condition and situation of the plane by engine vibrations, etc. To be caught with (one's) pants down "discovered in an embarrassing condition" is from 1932.
To be responsible for a defeat or other misfortune: did miss three free throws and came close to wearing goat's horns (1980s+)
ants, cream one's jeans, fancy pants, fly by the seat of one's pants, fudge one's pants, get the lead out, have lead in one's pants, high waters, hot pants, raggedy-ass, seat-of-the-pants, shit one's pants, smarty-pants