To say something that is often too personal, usually irrelevant, and always unfair. The expression comes from boxing, in which it is illegal to hit an opponent below the belt.
IQ Below room temperature, a phrase used to describe an individual who is so stupid that the temperature of a room is higher than their IQ Score.
This type of person should cause the standard human to be in pain just having to talk to an individual such as one described here.
*If someone that you believe to have an IQ below room temperature doesn't understand the phrase then they have confirmed your belief.
**Even more effective if you live in a country that uses the metric system!
Connor (Person with an IQ below room temperature): *says some dumb shit*
Ryan: Fucking hell Connor, you've got an IQ lower than the temperature in here!
(adj.) Below the line of what is acceptable behviour. Used to describe an insult that was a little extreme, but comes from physical fighting where Queensbury rules and broughton's rules dictate that no punches are to be thrown below the belt.