Heissing is the act of putting your asshole directly up to your partners and pooping back and forth. In order for this to work successfully a firm log is required.
Duuuude, my roomate and his girlfriend were Heissing last night. The whole house smeels now and he had to borrow a spareset of my sheets.
When you have so many assignments to do that you feel harassed and wonder if you could sue your uni while trying to find some help on Wikipedia a few hours before (sometimes after) the deadline.