Flash in: using Flash to jump onto an enemy and start a fight. Flash out: using it to escape. The same spell, two opposite decisions.
team chat
what you type
flash on him and stun
in full english
Flash onto him and stun.
the context
"flash on him" is an engage order, often to the tank. "he flashed out" explains a missed kill. A Flash spent going in is no longer there to get out.