They laugh at it or shrug it off because they know it's out of their control at that stage. If they could go back and fix animation errors and had all the program files, they would, but that would re-quire a LOT of re-rendering on an already short schedule and it just really doesn't allow for it, even though episodes are done for months in advance.
For anyone who hasn't worked in animation, people are well aware of errors. There's usually a dedicated person who goes through episode frame-by-frame and teams will end up looking at a single shot dozens of times during production and while some mistakes are simply missed, a lot of the time, mistakes are due to render errors that may have been noticed long after a shot has been rendered and there just simply isn't enough time to re-open the file, fix the mistake, re-render that shot, and then re-render it with the entire episode.
Then factor in that the majority of the time these shows are being made by Rough Draft Studios who have hundreds of projects on their hands and simply can't afford to be anal about every single show and every single frame and yes, these studios DO have a priority list for their shows. FOX ones that have the big money like Simpsons are given top priority. Flagship shows like Gravity Falls and Adventure Time have more focus put into them but still a couple of errors get by.
Then there are shows that are given less focus, like SU, PPG, Bare Bears, Uncle Grandpa. The reason PPG most likely has the most errors is because CN probably treats it more like shit and are being super stingy with their time and money while things like SU and Uncle Grandpa actually have some of the board artists doing a lot of keyframes which eases the workload. PPG boards are more traditional where they are putting a LOT of trust in the overseas animators.
Also most overseas animators don't give a shit, they're more concerned with meeting deadlines than perfect quality.