Custom Report - All Interesting Moments

It is not available.

You can look at Last Int Moment fields or use API.

Just to expand on Josh's comment, these kinds of cross-lead, activity-centric reports aren't available in the UI (a report of all form fillouts is another example).

But if you use the API (Bulk Export or Bulk Extract, the latter much easier) you can get at this remarkably easily. In many ways, the API takes the opposite angle on Marketo data from the UI. There are readymade views/exports via API that aren't possible via UI and vice versa.

One option is to create an "Interesting Moment History" field - where you store a continuous feed of IMs each time a new one is triggered; and an "Interesting Moment Score" field.  For example, here's how we capture these when someone attends an event:

The default choice value for when the IM is appended to the existing history value is as follows:

{{system.dateTime}}: Attended an Avanade Event: {{trigger.Name}}{{my.line-break}}{{lead.Avanade Interesting Moment History}}

You can then run a report where IM Score > 2 (to ensure your report only includes those people with at least 2 IMs).

We use the IM history field in both our reports and real-time alerts (to sales and marketing).  Here's an example of how this appears within our real-time alerts (we do the same thing for web page history):

Think of this as a poor man's way of reporting on Marketo Sales Insight (MSI) data without having to purchase MSI!

I presented on this technique at Marketo Summit (as part of my "Strengthening Sales & Marketing Alignment: Developing Real-Time Alerts with Rich, Actionable Insights" session).  Here's a copy of the presentation deck (which also includes a great tip provided by @Sanford​ on how to create a simple velocity email script token to insert hidden line breaks between each entry in your history field and make each entry readable within your reports/alerts).