loop-the-loop, n.² — Green’s Dictionary of Slang

loop-the-loop n.²

mutual oral-genital stimulation.

1971		E.E. Landy Underground Dict. (1972) 121: Loop-de-loop n. [...] Simultaneous oral-genital copulation between two people.
1972		B. Rodgers Queens’ Vernacular 182: to practice orogenitalism [...] loop-de-loop (late ’60s).