And unless you do something really bad, you'll just get PM privileges revoked.
you could send somebody a bunch of research that they didn't want; they'll report you, and you wont be able to pm anymore if badspot decides it should be that way
afaik, unless you do something seriously, seriously, horrible (probably illegal too), you aren't going to get an actual ban for anything you send in a pm
but if you're just sending a bunch of people messages about how much you like them or whatever, they most likely aren't going to report you for it, and I'm pretty sure badspot doesn't get involved in pms as long as nobody reports anything