This forum has been good for many things such as the introduction of the descriptive term donut bumper - decorated with the David Westheimer mark of excellence, no less - into my vocabulary (my protected upbringing had shielded me from this). Now I can add helmet humper, vielen lieben Dank.
Which reminds me:
My daughter Teresa had a group of tortoises as pets, these were sexually quite active all year round. Even at an early age, she was thus no stranger to the inner workings of nature. You know us, we were liberal parents.
When on an African vacation we visited a park located on one of the Seychelles islands that kept a group of (rather large) tortoises it became obvious that something (neck-biting, heavy breathing and hissing, the bumping of shells - really an orgy of reptilian scale) was afoot. A middle-aged couple, coincidentally German, did however misconstrue the scene and the wife said:
"Look at these two, they are fighting!"
To which my daughter, at that time seven or eight years old, helpfully conveyed:
"Naw, don't think so, they're screwing more like."
Her little brother Leon, back then about four to five years (and himself sexually active from a disturbingly early age), added his biological expertise:
"Definitely screwing, these people have no idea."
In stern silence, the German couple left the scene of our despicable failure as parents in a hurry.