PSA: New trick to ban yourself. Please read.

While many actions in the game do have a call and response from the server, it is believed that opening your inventory and equips is not one of them.

You can open your Inventory, Equips, and Walk around while the server lags and does not respond. You cannot however, talk to an NPC.

When the server lags, you stop receiving packets from it. So you can't do any actions that require an answer from the server (using buffs and potions for example). While you can keep doing ones that only send information, but don't demand any from the server (using attack skills, sending messages and opening UI windows for example).