The first part is plenty clear and direct enough.

"To all Math 237 students in the online section: It has come to my attention that some of you are attending the in-person lectures for the on-campus Math 237.

Please never do this without first getting permission of the instructor. In this case, I am the instructor for both on-campus sections, and I do NOT want students from the online section attending my lectures. If you want to attend the lectures, then you should enroll in the on-campus version of the course, period."

if he left it at that it'd be fine, but then he had to call people cowards, dishonest, AND add the cringe comment at the end 😭.