Slope off
Definition 1 of 1
Pro Tip 1/3Usually Unnoticed
The phrase often implies leaving without drawing attention, not simply exiting. 
During the chaos, Sarah managed to slope off to her room.
Pro Tip 2/3Slightly Negative
Can suggest avoidance of responsibility or leaving when it's inappropriate to do so. 
After messing up the work schedule, he sloped off before anyone noticed.
Pro Tip 3/3Colloquial Use
More common in casual speech among British English speakers. Not often used in formal writing or speech. 
I'm bored at this party; I might just slope off.