I'm conducting electrolysis of water with a 0.25M KOH solution in water (about 14 on my pH meter) using graphite electrodes, and I was wondering if the O2 would be safe to inhale, as in an oxygen bar?
No. Untreated and unpurified, the gas coming directly out of your reaction vessel would be unsafe to inhale. It is likely that water vapour containing traces of KOH would be present, and this poses a significant safety risk to the person breathing this vapour. You could test this yourself by measuring the pH of the headspace above your reaction vessel. Hold a piece of indicator paper here for a period, and it will slowly show a change.
The only thing in the gas phase at the anode will be pure oxygen, but when these small oxygen bubbles break the surface they create a fine mist of the electrolyte. This can be eliminated as an issue by running the resulting gas through a wad of cotton wool or a wash in water. There is, however, a different reason to be cautious.
At high enough partial pressures, oxygen becomes toxic to humans (really all life, but to different degrees). This becomes a major problem for deep scuba dives, divers have to reduce their oxygen to inert gas ratio beyond a certain depth.
For short exposure times, O2 partial pressures well above one atmosphere (~101.3 kPa) can be tolerated by humans, but on longer exposure times even O2 partial pressures as low as 30 kPa (about 30% O2 at sea-level pressure) have been known to cause issues for some individuals.
Because of this, I strongly advise against breathing pure O2 from any source for an extended period of time.