For large mounts - intentionally standing on people to disrupt activities Blizzard has been known to take action. For example they have no mount zones around certain vendors, quest givers, etc. Esp for holiday events.
In some cases, the RP disruption is severe enough the GMs do act on it. I have mostly seen that for weddings, funerals, and other organized in-game events that get plagued by outsiders.
Players can move though so are not stuck under something and have some defenses!
Baby Spice is a great one. Looks like garrison inn level 3 and the Dalaran cooking quest still give it.