A member of staff and you think you know
A member of staff but dunno who
a student (whos already on facebook)
a student (whos not already on facebook)
Some weirdo whos not even connected with the course
a figment of your imagination
The president of the RPSGB
some sort of ghost type weird spirit whos going to start picking off everyone who accepts him/her as a friend a bit like in the ring or some other rubbish horror film.