I have this theory that the degree to which a department is actually laid back is inversely proportionate to the degree to which it appears laid back.
The superficial things: people dressing more informally, faculty wearing flip flops and insisting that they be addressed by their first names, seem to be a sort of anxiety-driven defense mechanism.

The deeper aspects of being laid back are things like faculty generally being hands-off/non-micro-managerial, collegial relationships among faculty, lower competition, fewer ego conflicts etc. Generally, the more laid back a department looks, the more of this toxic stuff is going on underneath.

I think this anecdotal observation of mine can be explained with reference to the notion of high-paradigm vs. low-paradigm fields. High-paradigm fields are those where there is a lot of agreement on the fundamentals, more generous peer review practices (people erring on the side of acceptance for work they aren't sure deserves publication), fewer and less toxic political warfare between factions etc. Low-paradigm fields are the reverse. The hard sciences and engineering are generally high-paradigm. The humanities/liberal arts are low paradigm. The apparent laid-back-ness seems to be the opposite.