Romanized abbreviation for the Chinese slang term 我他妈射爆, which roughly translates to "I shot came so fucking hard." Is usually a stand-alone phrase.
Shoutouts to all the confused pornhubbers out there, here you go
wtmsb is Initial abbreviation of “我他妈射爆” ( wǒ tā mā shè bào ) in Chinese Mandarin . Usually use by weebs . When they surfing on the ACG forums and see some CGDCT anime characters but dont know how to figure out the Sexual impulse in their head , they will just post "wtmsb" .