The line comes from The Elder Scrolls IV: Oblivion, released by Bethesda in 2006, where Imperial Guards use generic combat barks during fights with the player. Oblivion's guards became a lasting meme source because of their serious delivery and repetitive dialogue, and short clips of their lines spread widely on soundboards and in gaming edits. This particular bark survived as a confident taunt, reused whenever a player wants to pretend an early loss was only a warm up round.
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Oblivion guard voice line 'I'm just warming up' from The Elder Scrolls IV combat, used when someone is confident and still just getting started.
This is a short combat voice line from an Imperial Guard in The Elder Scrolls IV: Oblivion, delivered mid fight with stubborn confidence. The guard says 'I'm just warming up' as if the battle so far was nothing, even when he is clearly losing. The delivery is earnest and slightly overconfident, which makes it funny out of context. Dropped over gameplay or real life clips, it turns a bad start into a boast, framing the speaker as unfazed, defiant and ready to keep going despite the odds stacking against them.