They're Coming is a screamer GIF that originated somewhere on 4chan, likely on /v/, in 2013. The GIF shows a comic where a sim wakes up to a phone call. The caller demands the sim to not open the doors of his house before abruptly hanging up, The rest of the comic shows the sim scared until the last panel where a figure with a knife is shown.
After 5 seconds, a flashing, red-tinted picture of Jeff the Killer pops up.
NOTE: The following GIF contains a screamer with flashing lights!