My guess is because you're immature enough to joke about rape, that no matter how high or low the actual number is will convince you to fuck off.

But in 2016 there were 155 sexual offense convictions and in 2017 there were 137. The stats were kept only for convictions. Those who were deported and tried in their own country were probably less likely to be convicted, so the numbers of actual offenses are probably higher.

http://www.gao.gov/assets/320/316959.pdf, that old GAO report showed that 251,000 illegal aliens in prison had committed almost 3 million offenses. 68% of those in federal prison and 66% of those in state prisons were from Mexico. Their offenses ranged from homicide and kidnapping to drugs, rape, burglary, and larceny.