Punny way to talk about getting with someone. The relation ship sets sail when people become unsure about the shore and sea the tides and times changin'. To be forced aboard the relation ship is to be stolen by pirates and held against your will. Often people will try and force you on a speed boat, but be sure to take your life jacket. Ultimately this ends badly; see the tale of Titanic, the epitome of rough seas and one will be forced to walk the plank. Often relation ships head towards Love Island (see Paul Danan), but there can be complications en route, such as an interfering 3rd party, known as an iceberg.
See also friend ship and companion ship
Check Jack and Rose getting aboard the relation ship. This probably won't end in Titanic.
Does anyone else want to potentially try and force me on the relation ship? ALL ABOARD, settin sail, bon voyage
Oh my cod, you're so shellfish, you will never get on the relation ship.