1) Accepting without proof 2) Arrogant 3) Assumptive 4) Excessively forward 5) Forward 6) Not checking to make sure 7) Presumptuous 8) Pretentious 9) Supposing 10) Taking for granted 11) Taking to be the case 12) Taking too much for granted 1) As if 2) Assumptive 3) Presumptuous 
• (p. pr. & vb. n.) of Assume • (a.) Pretentious; taking much upon one`s self; presumptuous.
As·sum'ing adjective Pretentious; taking much upon one's self; presumptuous. Burke. 
assuming Expecting too much of other people.
taking too much for granted; presumptuous.