A few tried to double down on their ignorance (not a great idea). Some snippets (via Romenesko):
@charlibobsss ("I fancy Zac Efron so so much") writes in three tweets: "For everyone saying what an idiot I am I'd like to 'educate' you all in saying I learnt of the titanic from watching a documentary of it, therefore I am not 'ignorant' in any way, shape or form :-) at the age of 16 it's not essential to know history like that, I've never seen the films either so it really isn't too much of a problem yep."
@lizamagang tweeted: "Got in the tosh.O blog for my titanic tweet. #embarrassing."
@iSophloveBieber tweeted: "Im glad im not the only who was shocked about the Titanic being real. Articles getting written and everything. omg."
@Jess_McBride ("I work in an ice cream parlour") tells one of her critics that "just because i didnt know that doesnt mean im thick." She later tweeted: "Just realised ive been walking around with a pen between my boobs for the last hour."
In case you missed the graphic: