Am I aloowed to vape a electric cigarette on tisha be’av the liquid is flavored but its only vape.
In general, it is not permitted to inhale water vapor on Tisha Be’Av (and certainly not on Yom Kippur), because the water vapor turns into water on contact, and one ends up drinking water, which is of course forbidden, and a Torah prohibition on Yom Kippur.
There is room to be lenient for the cigarette on Tisha Be’Av, provided that one does not swallow any liquid. The purpose of the “cigarette” is not to swallow anything, but only to simulate a cigarette, and therefore it can be compared to mouthwash and other liquids that are not supposed to be swallowed.
Therefore, one can be lenient.
For washing out one’s mouth, on Yom Kippur authorities are stringent (see 467:3; 613:4; 613:6 and Shaar Ha-Zion 20); on Tisha Be’Av, where a person experiences discomfort, one can be lenient.