unyielding — unable to bend or be penetrated under pressure; hard: trees so unyielding that they broke in the harsh north winds.
difficult — not easily or readily done; requiring much labor, skill, or planning to be performed successfully; hard: a difficult job.
inelastic — not elastic; lacking flexibility or resilience; unyielding.
intolerant — not tolerating or respecting beliefs, opinions, usages, manners, etc., different from one's own, as in political or religious matters; bigoted.
tense — in a state of mental or nervous strain; high-strung; taut: a tense person.
unflexible — capable of being bent, usually without breaking; easily bent: a flexible ruler.