(US, chiefly New York City) On a queue; waiting one's turn for something.

present participle of walk on eggshells

(slang) Less vulgar synonym of work one's ass off.

(idiomatic) To maintain one's concentration fixed on one important theme.

(idiomatic) To work especially hard, usually for an extended period.

(idiomatic) To be overly careful in dealing with a person or situation because they get angry or offended very easily; to try very hard not to upset someone or something.

(idiomatic) To lose one's concentration on what is most important.

To board a vehicle. / (idiomatic) To attack verbally, to criticise excessively. / (idiomatic) To take immediate action regarding; to avail oneself of without delay.

(reflexive) To serve oneself, especially to take food or other supplies, rather than wait to be served by another; used to indicate friendly permission or invitation.

(slang, postpositive) To a large degree, excessive. / Mobile; able to be moved.