I believe this is Navy trick to remember the trig functions, I'll try to explain, hopefully without pictures.

1. the trig functions apply to right triangles, (one 90 deg corner)
2. the leg opposite the right angle is always the hypotenuse.
3. from either the other 2 corners, the leg forming one side is adjacent
4. the other is the opposite.

with that in mind, take the first letter from the punch line to remember the trig function. sine = opp(Oscar)/hyp(Has), cos=adj(A)/hyp(Hat), tan=opp(On)/adj(Always)

So if you can remember sin,cos,tan and the Oscar Has A Hat On Always, a $5 scientific calculator and a scrap of paper you're in business.

For those more shop minded Hard is sometimes substituted with Hat