Probably the most malicious thing I've done with R

a_very_bad_thing.R

# operator that reverses the direction of assignment
# only if called from the global environment
`%>>%` <- function(x,y) {
  if(sys.nframe() == 1) {
    assign(deparse(substitute(y)), x, parent.frame())
  } else {
    assign(deparse(substitute(x)), y, parent.frame())
  }
}

# redefine the assigment operator and cover our
# tracks just to make it as nasty as possible
unlockBinding("<-", baseenv())
`<-` <<- `%>>%`
rm(`%>>%`)
lockBinding("<-", baseenv())