Charter member of the rodent club

[Hock9]

How do you guys handle a true "rat's rat", ie: someone who always has an "under his breath" comment every time he walks by, ie" something like "you're struggling today", or "I don't have to say anything to you, because the crowd's getting on you now", or other non-profane, immature, no-class, rodent-like comments (heard by no one else, with no overt overtures, no arm waving, etc)