A "thoughtless comment" refers to something that someone says without considering the consequences or being insensitive. It often hurts or upsets others unintentionally. Full definition
Yes, as I expected, your joke site still deletes and the sheep rule the roost with thoughtless comments about other sites. (realclimate.org)
Devastated by the loss and hurt by thoughtless comments she received from those who couldn't empathize, Tara reached out to other mothers who had experienced loss. (pregnancyafterlosssupport.com)
You have the right and the responsibility to yourself and to the memory of your treasured companion animal, be s / he cat or dog, bunny or bird, hamster or horse, to stop people who are intruding on your grief with thoughtless comments or questions. (aldf.org)