After reading this list you will have gathered that Culture ships tend to name themselves whatever the hell they like. However, you may be puzzled by the recurring appearance of the word "gravitas" in there. We've got the GCU Very Little Gravitas Indeed from Use of Weapons, the GSV Zero Gravitas in Excession, and the GSV Experiencing A Significant Gravitas Shortfall from Look To Windward.
Spotting this trend, a number of people questioned Iain M. Banks, the author of the Culture novels. He responded saying that it is basically a running gag within the Culture itself. One of the Involved civilisations (i.e. different civs which have an involvement with the Culture) found it a little surprising that ships with such awesome power and intelligence would be given names like I Blame Your Mother and Space Monster. Perhaps it would be more appropriate to choose names with a little more gravitas?
Supposedly one of the Culture ship manufacturies immediately responded to this by beginning to name all their newly-created ships No Gravitas Here, Dwindling Gravitas, Absolutely No You-Know-What and the like, and continued to do so for quite some time.
Banks claims to have a growing list of about 20 "gravitas" ship names at home, but no way to use them up until his next Culture novel.