Being someone's personal calendar

It's Tuesday and I'm supposed to be going out with DB.  There's been a lot of chat, but we agreed yesterday to meet up today after work.  We figured out the time (5 pm) since we'd both finish work.  I'd meet DB at Yonge and College Streets since it's midway between both of us.

As it gets closer to 5 pm, I wonder if DB is going to text me first, or of it's the other way around.  Five o'clock turns into six which turns into 6:30 pm.  I'm sick of waiting so I sent a text then asking if he's still working.

"Oh FUCK! I totally forgot!  I'm so sorry dude." The reply comes minutes after my message.

Really?  How forgetful can you possibly be?  We were just chatting, like, hours ago.

"To make up for the non-jerk behaviour, you're paying for coffee." I send a text, my reaction is totally justifiable.

Then, I get this.  "Ok, I'll pay for your coffee.  That's a given.  But why didn't I hear from you until just now?"  As if it's my fault to act as someone's personal calendar (not to mention assistant).  His cell has a calendar.  DB does everything with his iPhone.  He'd even shit with it if there was an downloadable app for that function.

I don't even bother to reply.  If someone doesn't have the common courtesy to schedule me in (let alone forget about me hours after chatting with me), then I have no reason to make time for them, either.