Green’s Dictionary of Slang

pucker up v.

[the facial expression involved]

to get into a bad temper, to become tense.

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[UK]Hotten Dict. of Modern Sl. etc. (2nd edn).
[UK]Sl. Dict.
[Aus]C. Crowe Aus. Sl. Dict. 61: Pucker, bad temper; pucker-up, to get in bad temper.
E. Shrake in Sports Illus. Jan in Davis (ed) Land of the Permanent Wave 158: ‘Nobody ever did it [i.e. ‘whip me’], but I sure got puckered up some’ .
[US]B. Moyers Listening to America 41: When one of those kids pucker up and want something, you’re going to give it to them, especially the girls.
[UK]Indep. Rev. 22 Mar. 5: At which point I pucker up.

In phrases

pucker up one’s asshole (v.)

lit. or fig. to tighten one’s rectal and anal muscles in preparation for a frightening experience.

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[US]J. Wambaugh New Centurions 329: ‘[P]ucker up your asshole and get a good grip on the seat because I’m telling you you aren’t going to believe this is America’.