Through the SBNation commenting system, users can, if logged in, recommend (or "rec") a comment they like or find enjoyable. If a comment acquires enough "recs" (five for EDSBS), the comment will turn green.
If a comment is particularly humorous or incredibly apropos for the situation, a commenter may say something to the effect of "Make it Plaid." Although currently there is no plaid setting for SBNation, such a remark is intended to connote that the comment is worthy of additional mention, above and beyond green.
Plaid is a reference to the Mel Brooks movie SpaceBalls.
There is currently no commonly accepted number of "recs" required for a comment to go plaid, though the general theory is twenty recs makes a plaid post.