sorry
I'm very sorry to bother you at this time of night.
I'm really sorry to bother you at work, but I just wanted a quick word.
Sorry to bother you, but I still have a few questions.
Sorry to bother you, but I couldn't help overhearing what you said.

SMART Vocabulary: related words and phrases

Making appeals & requests
adjuration
appellate
apply for something
apply to
ask a lot
besiege
car wash
cry
demand
entreat
imploringly
importunately
importunity
invite
invocation
leech
pester
push
scrounge
ticket

You can also find related words, phrases, and synonyms in the topics:

Making & accepting apologies