What is one fish that you wish you would have avoided from the start?

With all of the information online, maybe check and plan their tank stocking out before they get the fish at their local store. Although, that sometimes may not be the case when new fish are at the store, or there are bigger options than you thought. What doesn’t help, in a majority of cases, is when the information at the store doesn’t align with the true nature of the fish you are about to buy. What fish have you bought before, that you would recommend to avoid at all costs based on your experiences?