。
I can't even stand it myself.
Literal
Self [even-でも] patience [subject-が] cannot-do.
我慢ができない is the negative potential of 我慢する ('to endure, to put up with'), using the ~ことができる construction in its truncated nominal form ~ができる. 我慢 ('patience, endurance') is a central Japanese concept for bearing hardship without complaint. The sentence expresses that even the speaker can't manage to endure something — likely said in frustration.