The term monorailing is based on the struggle to establish a Washington State monorail, which had a very, very, very long history of the same. Many years of agreement that it needed to happen, but many, many, many years of discussion before it could happen.
Verb, "To monorail" - Sex act where two men stand facing each other with tips of erect dicks touching. One man moves his fist back and forth over both penises, from the base of his, to the base of his partner's, and so on. The fist is the monorail car, the touching dicks are the length of track.
"Dude... did you and James fuck yet?" "Naw, man. We did some monorailing, but that's about it."
The sexual practice of connecting two erect penises together at the tip whilst a fully lubed, double sided 'sleeve' fleshlight is made to move along one participants shaft to the others, sliding back and forth from one base to the other (Mimicking the movement of a monorail going from one station to another, hence the name)