Easiest way to spot plastic fans is if they start bragging about their club having more fans, proper glory hunting behaviour. These people deserve to be mocked relentlessly for caring about such inane stuff.
It shows how insecure Liverpool fans are though, everyone knows they are a bigger club than City yet their mutant fanbase still feel the need to belittle City every chance they get and tell everyone how bad their fans are etc and how much bigger they are.
This is why Liverpool fans are hated so much, not only do they constantly suck their own fanbase off 24/7 but they spend all the time when they are sucking themselves off trying to belittle on whichever team is currently doing better than them,