Most of the culture ships are named after punchlines to jokes about war, violence, and excessive use of force. There seems to be an implication in the novels that the names of GCUs are less violence oriented, but I can't find many examples. There is no direct back-story about these particular ship names, but with perhaps a few minor exceptions, Ian sticks to his popular convention of ship names that are usually punchlines and usually about warcraft or violence.
From Consider Phlebas, chapter 2:
By their names you could know them, Horza thought as he showered. The
Culture's General Contact Units, which until now had borne the brunt
of the first four years of the war in space, had always chosen jokey,
facetious names. Even the new warships they were starting to produce,
as their factory craft completed gearing up their war production,
favored either jocular, somber or downright unpleasant names, as
though the Culture could not take entirely seriously the vast conflict
in which it had embroiled itself.
ManyThe quote from Player of Games that mentions the ships:
"What are they called?'
"The Of Course I Still Love You and Just
read the Instructions."
"They're not warships?"
"With names like that? They're GCUs; what else?"
"Good," Gurgeh said, relaxing a little, looking out of the square again. "Good. That's all right." He took a deep breath.
Its been awhile since I read Player of Games, but I believe Gurgeh is relieved that the ships being contacted are not warships. This quote also seems to imply that some GCUs have more inane sounding names than the Warships. As far as I know there isn't much reference to the (subtle?) difference in naming beyond these quotes.
Many of the ships have anti-war views, but believe in the necessity of some violence to achieve a greater good. Thus the culture feels the need to let off angst about war in different ways and the names of the ships is one of those ways.
Many of the ships are only named in passing, or are on the sidelines of a conflict, so many ships are not always important characters in a story. Both ships are from Player of Games and are friends with one of the drone main characters. I can't recall offhand if they had any significant interactions and I can't seem to find any detail about it online.
From Consider Phlebas, chapter 2:
By their names you could know them, Horza thought as he showered. The
Culture's General Contact Units, which until now had borne the brunt
of the first four years of the war in space, had always chosen jokey,
facetious names. Even the new warships they were starting to produce,
as their factory craft completed gearing up their war production,
favored either jocular, somber or downright unpleasant names, as
though the Culture could not take entirely seriously the vast conflict
in which it had embroiled itself.