a cretin, an imbecile, someone who is so incompetent he/she is unable to expand 3(x+1). A remdot is a person who is susceptible to failing at life on a daily basis and making a fool of themselves whenever life gives them a chance to.
Remdot: yo how do I multiply fractions again?
Person: multiply the top and do the same for the bottom you fucking remdot.
Person: Ben failed his GCSEs, studied media studies and photography at A-Level and thought he stood a chance of getting into Oxford University. What a remdot.