WordNet sense 1 (of persons):

uncontrollable

WordNet sense 2 (difficult to manage or control):

unmanageable

WordNet sense 3 (hard to endure):

trying

WordNet sense 4 (difficult to deal with):

troublesome

WordNet sense 5 (bristling with perplexities):

thorny

WordNet sense 6 (very difficult; severely testing stamina or resolution):

tough

WordNet sense 7 (extremely difficult; requiring the strength of a Hercules):

herculean

WordNet sense 8 (unpredictably difficult in operation; likely to be troublesome):

fractious

WordNet sense 9 (difficult to handle; requiring great tact):

delicate, ticklish

WordNet sense 10 (making great mental demands; hard to comprehend or solve or believe):

knotty, problematic

WordNet sense 11 (hard to deal with; especially causing pain or embarrassment):

awkward

WordNet sense 12 (difficult to accomplish; demanding considerable mental effort and skill):

arduous

WordNet sense 13 (requiring full use of your abilities or resources):

ambitious

WordNet sense 14 (not easy; requiring great physical or mental effort to accomplish or comprehend or endure):

hard