Well an example for climate change might be that they go on about how important an issue it is, but don't make changes to their own lifestyles.
Often people will blame "the system" for environmental issues, and say individuals can't make a difference. But individuals make up the system. They create demand for unsustainable products and services. Even when they buy something sustainable, they consume more than they need/is fair They pay someone who profits from those things and produces more of them. Etc.
So someone who posts about recycling, or how great that David Attenborough programme was (who himself took long enough to say anything about it), but isn't vegan, and drives or flies, obviously doesn't have the courage of their convictions, and just wants people to think they're a great person without having to do the things that actually create change, or make what they perceive as a sacrifice.
There are also lots of people who change energy supplier to a supposedly sustainable one, but don't look into it any further than the marketing on the website. And then they announce it on social media, partly for recognition, and partly to share their rewards code (more consumption...).
Actually they're all energy resellers (Bulb, Octopus etc), and it makes no difference to how much green energy is produced if you use them; it just makes people feel like they've done something good. If they wanted to actually increase green energy infrastructure, they'd go with Ecotricity (or Good Energy, but I think the former is preferable for various reasons).