A forced meme is a "meme" that came to be through consistent posting of the "meme" by the creator of the "meme". Almost all forced memes are not actually memes. Nobody usually understands these, they are simply just there. Most forced memes get completely dumped into the dark corners of the internet, though some actually become famous and somewhat memetic. A prime example of a forced meme that actually became a meme is F**k Yeah Seaking. It started out as a forced meme on /b/ but eventually spread out to other sites and became a meme.
Milhouse was also a forced meme, but he became so forced that it became common to reply to a Milhouse picture with the statement "Milhouse is not a meme." That sentence in itself became a meme. Milhouse himself never became a meme.
Poster 1: Here's a picture of Milhouse. He is a meme.
Poster 2: MILHOUSE IS NOT A MEME. STOP POSTING THIS STUPID FORCED MEME!!1!!111!