KPMG is definitely a serious company and well-established player.
For sure it's not the primary choice for many candidates interested in general management consulting - but many candidates are also attracted too much by the big MBB brand names and focus too little on what actually fits their preferences better.
If somebody makes fun of KPMG and means it in a serious way, I am not sure if I would have a high opinion of a person looking down on somebody/something else in general...
Hope this helps - if so, please be so kind and give it a thumbs-up with the green upvote button below!
Finally, for your amusement only - when I was at an South African client last time, a collegue told me innocently: "Look out of the window, [BIG4 - I removed logo in pic] is full of monkeys!"