Branding
Branding
Browsing without adblock [Cueball is sitting at a computer.] [Pop-up window with red background.] The Facebook of SEX! Click now! Cueball: Sigh. *Close*
[Pop-up window with green background.] Twitter for 18+ singles! Join today! Cueball: Does every porn site have to brand itself like this? *Close*
[Pop-up window with blue background.] We're like Google Reader for S&M! Cueball: Really? *Close*
[Pop-up window with orange background.] Try the new GitHub for lesbians! Cueball: Ok, wait, what?

This comic pokes fun at web sites (adult-themed sites in particular) which try to inflate their popularity by comparing themselves to other popular online services.  The strip shows four such advertisements that appear to Cueball as he browses the Internet.
Adblock is a browser extension which prevents advertisements from being displayed. Presumably Cueball normally browses the Internet with Adblock enabled, and thus would not see any of these ads.
The first advertises a website that brands itself as the " Facebook of sex". Because Facebook was ubiquitous at the time of writing, this is a good branding idea. Facebook is known to most users and connotes an easy-to-use platform where it's very easy to find people, chat with them, share pictures, etc. For someone looking for sex, this would probably seem like a good site to use. There are, in fact, sites that use this branding in their advertisements and/or their user interface which is likely what inspired Randall to write this comic. Cueball sighs and moves on, probably having seen this kind of ad many times already.
The second brands itself as "Twitter for 18+ singles". It is a similar but seemingly invented ad which again plays on the ubiquity and popularity of Twitter , which is a (generally) public chat forum. Despite the fact that, at the time this comic was published, it was limiting posts to 140 characters, it was still popular enough to get some attention and make someone think about going to the site.  Sending messages to the world in 140 characters or less might be somewhat less of a versatile platform than Facebook for chatting with other singles, but still perhaps viable. Cueball notes that it is becoming more and more popular to brand adult sites by comparing them to popular non-adult sites.
This third takes a turn for the unusual, branding itself as "Google Reader for S&M". Google Reader is a now-defunct platform that allowed users to aggregate web feeds such as RSS feeds into one place for convenience. The service is notably less well-known and popular than Facebook or Twitter, and given that it doesn't directly link you with other people, doesn't have the same connotation of allowing you to connect with others. Perhaps it would be a site that allowed you to aggregate various fan fictions, blogs, or other written works relating to S&M . However, Cueball is surprised such a site would exist.
The final ad brands itself as a "GitHub for lesbians". GitHub is a website that allows developers to collaborate on software projects using the Git revision control system. The concept is absurd — GitHub has a specialized function unrelated to anyone's gender or orientation, and it's barely a social network at all; the usefulness or appeal of such a system made specific to lesbians is not apparent. Cueball is surprised and possibly even intrigued by this last ad.
The title text relates to the third panel. RSS is a technology involved in Google Reader. RSS&M is a portmanteau of RSS and S&M.  This is a possible way for the third web site to brand itself.
Browsing without adblock [Cueball is sitting at a computer.] [Pop-up window with red background.] The Facebook of SEX! Click now! Cueball: Sigh. *Close*
[Pop-up window with green background.] Twitter for 18+ singles! Join today! Cueball: Does every porn site have to brand itself like this? *Close*
[Pop-up window with blue background.] We're like Google Reader for S&M! Cueball: Really? *Close*
[Pop-up window with orange background.] Try the new GitHub for lesbians! Cueball: Ok, wait, what?
