The prank, which happened in a corridor at Benfield School, Newcastle upon Tyne, left the teacher deeply traumatised when she found out the picture posted on the Internet, as she had unwittingly used the cup afterwards, reports the Sun.
The school's own investigation revealed the student who took the cup had been urging friends on Facebook to dare him to carry out risky or bad-taste pranks.
"The boys saw the cup in a classroom which they then took. They did the deed in the corridor. It all came from one of them on Facebook asking his friends 'Who dares me to do this....," said a source.
"The upshot is one of them has been permanently excluded and three are on fixed-term exclusions. The authorities have decided it was horseplay that got out of hand," he added.
It is understood the teacher was off work for some time after the incident. (ANI)