Pi r squared and 2 pi r - completely useless in my 55 years but I still remember them, as loads of other equations, too such as Ke=1/2mv squared. Also bil and bev but havn't the foggiest what they were about (I don't think I did at the time either) - something to do with electrical forces (A level physics).
SOHCAHTOA obviously - something else completely useless in adult life.
Krankenwagen - German for ambulance, Krankenhaus - German for hospital. Geschlect - German for sex.
Dulce et decorum est pro patria mori - can't remember anything else about the poem.
"eloi eloi lama sabachthani" - literally the only thing I could ever remember from Religious Studies O Level - I got grade U twice (the sods made me do it again the year after!).
My greatest success is being able to recite "the naming of cats" by TS Elliot - I can still recite it today, decades later. I don't even like cats, but our English teacher spent lesson after lesson, week after week, forcing us to learn line by line for CSE Eng Lit. Trouble was, we never really learned what it was all about, so despite being able to recite it, the whole class was abysmal at answering questions on it!