I'm not sure what you mean in this context by decadent. However, a key difference is that democracy is more than majority rule.
Ochlocracy is the rule by the majority. Democracy is much more. Definitions vary, but democracies have constitutions protecting citizens rights, civil liberties, rule of law, equality before the law, and other rights. Those rights cannot simply be voted away by a simple majority. In a well-functioning democracy, such rights are safeguarded. Quoting the Wikipedia article on democracy:
While there is no universally accepted definition of "democracy," equality and freedom have both been identified as important characteristics of democracy since ancient times. These principles are reflected in all all citizens being equal before the law and having equal access to legislative processes. For example, in a representative democracy, every vote has equal weight, no unreasonable restrictions can apply to anyone seeking to become a representative, and the freedom of its all citizens is secured by legitimized rights and liberties which are generally protected by a constitution.
In my interpretation, a democracy is degenerating into an ochlocracy if it takes away those properties of democracy other than majority rule.
Precise examples are likely to be subjective. Some examples include:
In Switzerland, a November 2009 referendum introduced a ban on minarets. This might be considered a degeneration into ochlocracy, because it is a majority rule in direct democracy taking away a particular right of a religious minority (to build houses of worship in their own preferred style). Some examples of articles exploring whether or not this is a degeneration into ochlocracy can be found here and here.
According to this blog post (frankly a bit of a rant), the Patriot act is an example of what it calls mobocracy, because a parliamentary majority decides to take away what it describes as many fundamental rights.
The same blog post describes as such the war against Iraq. I think it argues that the war against Iraq was authorised despite being illegal.
On the other side of the political spectrum, popular nationalisation of foreign assets could probably be described as ochlocratic. I'll search for a source to back this up
Perhaps any majority decision one disagrees with could be described as ochlocratic. For example, Conservapedia describes Wikipedia as ochlocratic, without explaining why.
I'm sure there are many more examples that can be given across the political spectrum. I'll do an attempt to summarise the symptoms, based on my own interpretation of the examples abowe:
Decisions by parliaments or referendums are taken as absolute and more important than the constitution, international treaties, or other fundamental laws.
In political debate, one hears increasingly often arguments that boil down to the voter is always right.
Minorities or arguments by experts are set aside in favour of the vox populi, the opinion of the man in the street.
There are probably other aspects that I'm not thinking of right now.
I don't have sources to back up the symptoms; the sources that I could find all relate to specific examples.