Whoever did this obviously feels pretty strongly about McGargles. Pity they are too cowardly to expose themselves to return fire.
I find the branding cringe-inducingly bad myself but I can't fathom someone going to the point of defacing packaging at point of sale.
McGargles is Irish Craft Beer. If you don't like the beer or the branding, don't buy it. Feel free to mouth off about it in the pub, or here, or on one of the many social media platforms out there. That way others can agree, disagree, or tell you you are being a wanker, which you most certainly are.