Laudator Temporis Acti

The Wikipedia article on wedgies doesn't mention the self-inflicted kind described by Martial 11.99 (tr. D.R. Shackleton Bailey):

Whenever you get up from your chair (I have noticed it again and again), your unfortunate tunic sodomizes you, Lesbia. You try and try to pluck it with your left hand and your right, till you extract it with tears and groans. So firmly is it constrained by the twin Symplegades of your arse as it enters your oversized, Cyanean buttocks. Do you want to correct this ugly fault? I'll tell you how. Lesbia, I advise you neither to get up nor sit down.

De cathedra quotiens surgis -- iam saepe notavi --,
  pedicant miserae, Lesbia, te tunicae.
quas cum conata es dextra, conata sinistra
  vellere, cum lacrimis eximis et gemitu:
sic constringuntur gemina Symplegade culi
  et nimias intrant Cyaneasque natis.
emendare cupis vitium deforme? docebo:
  Lesbia, nec surgas censeo nec sedeas.

The Oxford Companion to Classical Literature, s.v. Symplegades:

the 'clashing' ones, also called Kuaneai [Cyaneae], the 'dark-blue' ones, two fabulous rocks that stood in the sea at the N. end of the Bosporus, forming the gate to the Euxine Sea. They were believed to clash together, crushing ships that passed between them.