I can turn that right around:
"Fat privilege is not constantly worrying about if you're going to be raped at any second."
CHEK UR PRIVLEG!!!
Except the person never said that being assaulted was a thin privilege, and it's kind of fucked up to assume that a woman won't be/has never been sexually assaulted just because she's fat. The way the post was worded is pretty bad, but the point she made is a fair one.
Okay, yeah, reading it more carefully it seems she was complaining more that someone
said that nobody would want to drug her due to her weight rather than complaining that no one would want to sexually assut her. I agree, that point is a bit better.