Ficher
"Ficher" has two meanings. The first means to write on a card. The second, more familiar, means "to do".
It is in its second sense that "ficher" has a peculiarity: being the only French verb that does not contain an infinitive with letter "r". Indeed, this verb is also written "fiche" in the infinitive. It is found, for example, in the familiar expression "Rien à fiche". It is always classed among the verbs of the first group.
If one day, you are asked what is the only verb in the infinitive French that does not contain letter "r", you will knwon the answer !