It's not a good idea.
Modern CPUs run pretty hot.
What temp do you think it can safely run?
Computers these days have built in shut offs if the CPU starts running hot. Not a good idea to rely on that shut off too many times. Now I don't think 80 degrees on a home machine is that critical, I've run mine in much warmer conditions, numerous times, without incident.
If you're worried about it open the side panels and put a small fan up against it blowing air through it, you can always clean (vacuum) the computer out later.
I agree. 80 isn't all that critical. I've run a couple of systems in temps approaching 90.
However, if you are concerned, you can open the side panel and point a little desktop fan into the box to help with cooling.
Oh, and while you in there, vacuum out your dirty computer you slob!!!
LOL
People never do and dust is a bigger enemy to your computer than heat in some ways.