You'll need to create a smart list with a bunch of the inactivity filters, such as the following:
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Not Clicked Link in Email
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Not Clicked Link in Sales Email
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Not Visited Web Page
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Not Activity was Logged
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Not Filled Out Form
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Not Voted in Poll
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Not Sent Forward to Friend Email
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Not Shared Content
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Last Attended/Registed: in past 3 months [custom field]