You know your lab is too warm when...

Your low melt agarose does.

From the seemingly defunct online science humor journal, Aliquotes

More answers to this:

You know your lab is too warm when...

No matter how often you fill them, your ethanol bottles are always empty.

You can heat-shock your bacterial transformations on your bench.

The gas from a bunsen burner spontaneously ignites.

You put your plates in the incubator to cool them down.

And a few more answers. Feel free to add your own!

You know your lab is too warm when:

Every time you open the fridge door, it rains.

A pellet of dry ice has a half-life of 12.3 seconds.

The Taq polymerase begins to denature.

The glucose in the chemical cabinet begins to caramelize.

....
When SDS-Acrylamide gels gets polymerized in mins, :)
When you can't bear your Lab coats anymore,
...

When your knowledge of quantum physics is now not an absolute zero

you know your lab is too warm when
sweat starts to add to the nutrients in your microbial medium
your computer shuts down before the UPS drains out