The humor comes from the relatable exaggeration of someone being so obsessed with tanning that they would consider it even in heavy rain, playing on the common trope of tanning enthusiasts.
Summary
The video shows a person looking out at heavy rain, with on-screen text humorously labeling them as "that one friend obsessed with tanning." The person comments on the rain, implying they would still be out tanning despite the weather.
Structure
1Person looks out at the rain
2On-screen text identifies them as a tanning enthusiast
3Person comments on the heavy rain
4Person speculates about the UV index
On-screen text
That one friend obsessed with tanning
Transcript
Damn. It's really coming down out there. Think the UVs high.