Nerd Rage!

Nerd Rage! is a perk in Fallout 3, Fallout: New Vegas, and Fallout 4.

Fallout 3
Whenever your Health drops to 20% or below, your Strength is automatically raised to 10 and you gain 50 to damage resistance. This stacks with other perks, and applies regardless of clothing, which makes it still useful even if you wear heavy armor, as it can help maintain your DR even if said armor is damaged or broken.

Fallout: New Vegas
Whenever your health drops to 20% or below, your Strength is raised to 10 and your damage threshold is boosted by 15. As in Fallout 3, this effect stacks with similar bonuses, and applies even if you're naked or your armor is broken; you merely need to meet the health threshold.

Notably, the Courier's base health determines the trigger for this perk. Bonus HP from other sources such as Buffout will not raise the threshold.

Fallout 4
When your health drops below 20%, you enter a Nerd Rage! Time slows down (similar to the effect of Jet), and you gain 20 Damage resistance and 20% bonus damage with the first rank. The second rank raises the extra damage resistance to 30, and you do 30% more damage. The third and final rank increases the damage resistance to 40, and you do 40% more damage. Additionally, killing enemies restores lost health.

Behind the scenes

 * The perk is based on Adrenaline Rush, a perk which had first appeared in Fallout 2. The art is also borrowed from Adrenaline Rush, save for a few thematic changes.
 * The Vault Boy image is a reference to the Incredible Hulk, whose clothes become shredded during his transformation.