There is no excuse for IIMC....ever.
Well, sometimes 5h1t just happens.
I was working on a massive bushfire in the Blue Mountains, when I was tasked to go from the south side of the fire to the north side. The only way in all that smoke was to follow the vertical sandstone cliffs (about 3500' here, tops in smoke) around the edges of the smoke-filled valley. I was sneaking along at about 40kt with very limited vis, using the cliffs outside my window for reference, when my windscreen was filled with a SeaKing doing the same thing in the opposite direction. He was marginally closer to the cliffs than I was, so the only thing to do was a snap turn to the left, out into the smoke. Dunno if he saw me or not.
Instant IMC. Onto the clocks, get power up to max, accelerate to 60kt and climb at the speed of stink, highest hill around 4000' but unknown position (before the days of moving maps.) All the smoke rising had turned into a big cumulus, so it was well over 6000' when I popped out into clear air.
Luckily I had a lot of instrument experience, and the aircraft was NVFR equipped, so I was relatively comfortable in the soup.
But I reckon that in this case, I had an excuse.