Squeaky Bum Time

A tense situation in the sporting world, namely football (soccer)
However it can be applied to various scenarios.
Carp fishing example:
When you are reeling in a large carp that is putting up a fight, the tense situation of reeling such a large fish in.
A famous fish that causes squeaky bum time is the Tuna or Lil's Lin or that little koi that follows dropscale

when you're hungover as shit after a spending a night drunk as a skunk

Squeaky bum time: The period of time, normally towards the end of a tense and pivotal football match, where nerves are high and people risk shitting themselves in expectation of the outcome.

the tense final stages of a league competition, especially from the point of view of the leaders, usually used in football (soccer)

Old Glaswegian saying for "On the verge of shiting yourself", commonly said in the closing stages of a football match when their is a one goal difference between teams, and the other team is going hell for leather in an attempt to score a goal.