Portable jokes are lines or bits that transfer across many unrelated situations and reliably get a laugh, per 4 Jokes That Make Women Notice You (Charisma on Command). Unlike Building a Fake World (Absurd Premise Stacking) (built fresh from whatever premise is in front of you) or Prepared Playful ("Home Run") Answers (tied to specific opener questions), portable jokes are pre-formed material redeployed wherever a matching situation arises — including repeatedly across different conversations.
Sourcing heuristic given: pull from lines you personally loved the first time you heard them. The host cites reusing Step Brothers quotes as his own example.
This is a stockpiling strategy — build a personal repertoire once, then draw on it opportunistically, rather than generating novel material in the moment for every situation.