Catchy and socially beneficial as it might be, I have a bit of a problem with this slogan.
It certainly seems that society benefits a tiny minority far more than the rest, though the real situation is probably a bit more complicated than harming 99% of people while benefitting 1%. Still, this lack of detail is forgivable: almost by definition you can't expect slogans to be nuanced, and it is probably doing enough movement-galvanising good to offset its misleadingness.
My issue is with student activists who identify as members of the harmed group rather than the benefitters: by and large I think they are wrong. It seems to me that, if you are a student at a high-prestige university, either in the UK or in America, then you are probably not in the bottom 99% for society's impact on your overall life prospects.
For one thing, you have the option of quite easily joining the financial benefitters by following some fairly simple and googleable steps. Most of the activists I know are clever, sociable and non-disabled etc enough that, with the help of their pieces of paper, they could (and who knows, maybe will) secure top-income-percentile jobs if they really wanted. In my opinion, possessing this option puts you in the top 1% whatever your actual lifetime earnings: most people don't get the luxury of choosing between tremendous incomes and fulfilling lives.
On a global level, the idea that a significant number of top-university students in the UK/USA are in the losing 99% is just silly, and when you think about countries with wars and famines, or where large numbers of people can't even afford running water or mosquito nets, it is actually a bit perverse.
More generally, I think there is a quite deep effectiveness vs beauty issue here. It is far more effective sales tactics for the spokespeople for an oppressed group to be members of it themselves, but often it just isn't the case. Being a spokesperson and a genuinely oppressed person at the same time is quite difficult as it requires lots of free time, education, charisma-development opportunities, powerful friends and other things that tend not to be available to the genuinely oppressed. This problem can be overcome by pretending to be oppressed in the style of Gandhi, but there is something really ugly about doing that I think.
Then there is the whole animal rights thing...