How to turn off snippets in Atom?
Sadly, there's currently no built-in feature for this kind of thing.
Until some filter feature is added to the snippets package, the only way to access the snippets is to monkey-patch the package from your init script.
For instance something like that will allow you to filter the snippets returned for a given editor at runtime:
# we need a reference to the snippets package
snippetsPackage = require(atom.packages.getLoadedPackage('snippets').path)
# we need a reference to the original method we'll monkey patch
__oldGetSnippets = snippetsPackage.getSnippets
snippetsPackage.getSnippets = (editor) ->
snippets = __oldGetSnippets.call(this, editor)
# we're only concerned by ruby files
return snippets unless editor.getGrammar().scopeName is 'source.ruby'
# snippets is an object where keys are the snippets's prefixes and the values
# the snippets objects
console.log snippets
newSnippets = {}
excludedPrefixes = ['your','prefixes','exclusion','list']
for prefix, snippet of snippets
newSippets[prefix] = snippet unless prefix in excludedPrefixes
newSnippets