enfoirer

A crude, informal verb rarely used in its plain infinitive form — its past participle enfoiré(e) is the truly common word, a vulgar-but-everyday insult roughly equivalent to "bastard" or "jerk."

• Cet enfoiré m'a doublé dans la file d'attente. — That jerk cut in front of me in line. (vulgar/informal)
• Arrête de m'enfoirer la vie avec tes retards. — Stop screwing up my life with your lateness. (vulgar, rare verb use)
• Espèce d'enfoiré, tu m'avais promis de venir ! — You jerk, you promised me you'd come! (vulgar/informal)

The verb itself is rare — what learners will actually encounter constantly is the adjective/insult enfoiré(e), which is vulgar but common in casual French, not obscure slang.

• expression Les Enfoirés — The name of the French all-star charity supergroup founded by comedian Coluche in 1985 to support the Restos du Cœur food-aid charity — a self-deprecating, tongue-in-cheek use of the insult that's now a beloved annual TV and album tradition in France.