I've never even played Portal (am hoping to get the free download while it's still available for the next week), so I was really thrown off. (Btw, if you need the info on the download, let me know, and I'll dig it up.) But it looks like the joke is referring to a game called Half Life (http://community.livejournal.com/damned_lounge/2246218.html?thread=33123146#t33123146) instead, anyway.