FID is the acronym for "fatty in disguise". A fatty in disguise is usually a woman who uses deceptive tactics to conceal her large body mass. She will often wear black to slim her figure or wear large multicolored garments as a distraction to her prey. When online, the FID will often take pictures at awkward angles and these photos will usually only be head shots.
With practice and experience, a man can quickly spot a FID and avoid wasting his time and energy.
"Mary's online dating profile looked really good, and she had a lot of nice headshots. I enjoyed talking to her on AIM and the phone. But after doing some stalking on google, I found out that she's really a FID, a fat, wretched, beast of a woman."
"That girl has big tits but its just all fat, take a closer look past that floral pattern on her dress, she's a FID man! Don't do it! "