Psych doesn't like backticks such as `

[lukaso]

As already documented at this issue on rubygems:
rubygems/rubygems.org#358

$ gem install git-branch-delete-orphans
Fetching: git-branch-delete-orphans-0.0.2.gem (100%)
/Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych.rb:148:in `parse': couldn't parse YAML at line 22 column 13 (Psych::SyntaxError)
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych.rb:148:in `parse_stream'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych.rb:119:in `parse'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/psych.rb:106:in `load'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:488:in `from_yaml'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/package/tar_input.rb:190:in `load_gemspec'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/package/tar_input.rb:55:in `block in initialize'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/package/tar_reader.rb:64:in `block in each'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/package/tar_reader.rb:55:in `loop'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/package/tar_reader.rb:55:in `each'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/package/tar_input.rb:35:in `initialize'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/package/tar_input.rb:20:in `new'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/package/tar_input.rb:20:in `open'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/package.rb:44:in `open'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/format.rb:62:in `from_io'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/format.rb:46:in `block in from_file_by_path'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/format.rb:45:in `open'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/format.rb:45:in `from_file_by_path'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/installer.rb:119:in `format'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/installer.rb:129:in `spec'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/installer.rb:386:in `ensure_required_ruby_version_met'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/installer.rb:156:in `install'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/dependency_installer.rb:297:in `block in install'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/dependency_installer.rb:270:in `each'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/dependency_installer.rb:270:in `each_with_index'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/dependency_installer.rb:270:in `install'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/commands/install_command.rb:121:in `block in execute'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/commands/install_command.rb:115:in `each'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/commands/install_command.rb:115:in `execute'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/command.rb:278:in `invoke'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/command_manager.rb:147:in `process_args'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/command_manager.rb:117:in `run'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/site_ruby/1.9.1/rubygems/gem_runner.rb:65:in `run'
    from /Users/loberhub/.rvm/rubies/ruby-1.9.2-p290/bin/gem:25:in `<main>'

[tenderlove]

Graves are reserved. The example YAML in the rubygems ticket is invalid (according to the YAML spec) and should be rejected.