Is It Presumptuous to Pat your Pretty Posterior?

A while after recovering from the dino-smut, my housemates and I resumed our typical nerdy grammar/word usage conversations. ("Why is pants plural?) Yes, it really gets us excited. Yes, we're really that lame. Lately, I've been using the words "assume" and "presume" interchangeably, inexplicably favoring "presume" as my word of choice. Though I knew there was some sort of distinction between the terms after having looked it up in another fit of nerd-dom, I had since forgotten and was trying to remember the difference. Someone thought they were exact synonyms, but Jessica hypothesized that "presume" had to do with being rude in one's assumption, hence the reason there is a word "presumptuous" and not "assumptuous." I giggled, imagining that ass-sumptuous would probably be a synonym for bootylicious. Surprisingly, I found that Urban Dictionary confirms my conjecture; "That girl is assumptuous!" is the example sentence.

Take note: From now one when you dare to make an ass out of u and me, I will call you "assumptuous" - then stare at your butt.