As a general rule, statements like "failing at life" (in relation to other posters) are frowned upon. You can call their argument stupid, you can call [insert thing person likes] terrible, but you should try to avoid directly casting aspersions on the people who are making those arguments or enjoying those things.
Good Example: "Knack is terrible and I don't understand how anyone could like it."
Bad Example: "Knack is terrible and everyone who likes it is clearly a blithering idiot."
Please note these statements are for example purposes only. I have not played Knack and have no opinion on it, or the people who play it. Offer void in AL, TN, SC, and VA.