RadToolTip and RadToolTipManager both support the same client-side events that let you customize the behavior of the control:
OnClientBeforeShow occurs just prior to the display of the tool tip.
OnClientShow occurs as the tooltip is displayed.
OnClientBeforeHide occurs just prior to the tool tip being hidden.
OnClientHide occurs as the tooltip is hidden.
For a live example illustrating the RadToolTip client-side events, see the Client-side events live demo.
The RadToolTipManager also offers three additional events that are specific for its Load-On-Demand functionaliaty:
Read more about them in the ToolTipManager Specific Events help article.