A ciggy butt is definitely litter, it's rubbish that you've dropped on the ground and IIRC they've been shown to not biodegrade in any reasonable timeframe under normal circumstances.
If it was cigarette or pipe ash I'd possibly argue slightly differently.
because it's waste, non biodegradable, and you're throwing it on the floor.
It's not really any different to a sweet wrapper or your polystyrene cup/burger box except for the size.
Or a leaf.
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