This may sound harsh, but......What is he? In
kindergarten? He had to go with his friend when his friend got an oil change?

And men laugh when women go to the ladies room together...... From the time I was 16 and got a car, I have been able to go into the big, bad world and get my car's oil changed by myself, without the aid and comfort of a buddy. I have never heard a MAN use this pathetic excuse.
As for having to go get haircuts together.....I can barely even type that.

Did they want matchies? They waited 90 minutes? A woman with long, flowing locks would be hard-pressed to wait that long. And your DH (at this point, it does NOT mean dear) didn't even manage to get that stinking haircut in 3.5 hours. For crying out loud, he could have let goats gnaw on his head and gotten a haircut in under 3.5 hours!
As some have pointed out, this isn't about a haircut or oil change. This is about guy who seems to place NO value on spending a rare family day with his wife and child. Although he gets to spend a lot of time with his friend (more than with his wife, it seems), he just CANNOT get enough of being with his buddy and will ditch his wife in a heartbeat if the friend needs to do something vital like gas up his truck or change the line in the weedeater.

He puts the OP in the position of either allowing him to completely get away with this (thereby sending the message to the OP and his child that a day with his son and wife is nothing compared to a day with his friend) OR antagonizing her enough to make her call and pester him about coming home. Then HE can play the victim.
This would NOT fly in my house. No way, no how.