#HaveAWank was a meme perpetuated by Dan during the PC Gaming part of the E3 livestreams. It was thought up by Dan who asked members of the audience if they were there to shout 'Have a wank!' as he was becoming bored. A short time later Matt placed 'Have a wank m8' and then '#HaveAWank' across the screen in large text which produced a large reaction in the twitch stream.
Throughout the stream the text was placed above the screen, and flashed at people, the fans in the stream of course jumped on this joke and began to spam the hashtag at every member of the stream, as a result it gained traction and popularity. Matt & Dan began to ask people to direct the hashtag at different people on Twitter including different YouTubers and then-British Prime Minister David Cameron.
The Hashtag was also spammed in the official PCGamer stream chat. It proceeded to trend worldwide on Twitter and has become a private joke between many members of the community.
This was originally a reference to the live shows of the sitcom Bottom starring Rik Mayall and Adrian Edmondson in which audience members would regularly shout out "Have a wank!" when the characters ask the audience what they should do.