DUCATI - 90th Anniversary

Place 3rd in at least 40 events
Ride a single bike for at least 100km
Ride a total of 200km
Unlock all Events and Bikes
Place 1st in at least 15 events
Complete 20 Online races (this one is very glitchy, only counts if you win and even then some races won't count)

This was pretty much a copy paste from x360a roadmap. Now on to the most important part:

If the achievement doesn't unlock after getting all the titles, press the guide button, go to your account. My Profile - Gaming.
On the gaming tab there the achievement should unlock.