Cinnamon rolling is a handshake whereby two or more people all put their right hands in together so their fingertips touch, wiggle their fingers then cry "CINNAMON ROLLLLL!" while curling their arms round so that all participants are making a big spirally shape with their arms. It was introduced by the Australian psych band Pond, and has since been adopted by UK bands Swim Deep and Peace among others, often as a pre-show ritual.
For an example, see Freshly Squeezed's interview with Swim Deep on youtube, skip to 3.13.
Great for making friends with people at gigs "Hey guys! Cinnamon rollll!" At this point they either have no idea what you're on about (in which case explain) or they do, and you bond over this shared piece of pop culture knowledge.