Green’s Dictionary of Slang

blow off v.2

[blow off n.1 (1) / blow off steam under steam n.]

1. (also blow it off) to release pent-up emotion.

[US]Ade Knocking the Neighbors 227: Father got so steamy that he had to blow off.
[UK]K. Williams Diaries 3 June 214: We had the cocktail party with the Captain. Handshakes & bonhomie. Me blowing off v. liberally.
[US]Baker et al. CUSS 83: Blow it off Go wild.
[US]G. Cuomo Among Thieves 173: Everybody started chickenshitting around then, razzing and blowing off.

2. to get angry (with).

[US]E. Townsend Chimmie Fadden Explains 84: His Whiskers had blowed off de mug at his house here, and his club [...] but in England de mug never blowed off his Whiskers, but only just called on him and Miss Fannie onct.
[UK]Burnley News 28 May 12/3: The welfare department provides a useful safety valve for the ‘blowing off’ of complaints and grievances.
[Aus](con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: blow off [...] To voice ones [sic] anger.
[UK]J. Worby Other Half 50: What are you blowing off about?
[US]J.T. Farrell ‘Milly and the Porker’ in Amer. Dream Girl (1950) 197: Never mind blowin’ off. You know goddam well he’s got your number.
[US]E. Gilbert Vice Trap 13: If I blew him off he would send the work to the Shell across the road.
[US]F. Kellerman Stalker (2001) 311: Did you blow off anyone in the last few weeks.

3. (US gay, also blow off steam) to achieve orgasm.

[US]B. Rodgers Queens’ Vernacular 34: blow off [...] blow off steam (les sl) experience orgasm.

In phrases

blow off at the mouth (v.) (also blow off at one’s head, blow off one’s mouth) [sense 1 + SE mouth/head]

to talk loudly or aggressively, to boast.

[US]W. Guthrie Bound for Glory (1969) 20: Quiet down! You damn bunch of liars, you! Blowin’ off at yer head what all you can do! I hear this talk all up an down these railroads! [...] You go around blabbin’ off at your mouth.
[US]B. Catton Army of the Potomac 150: [A] hard-fighting, distinguished soldier who just has to blow off at the mouth every now and then.
E. Brandon Green Pond 303: Now, if you want to blow off at the mouth, get up there in the pulpit and flail the devil out of them.
J.A. Walker River Niger 30: ann: Blow off at the mouth! Blow off! Blow off! Pardon me, but kiss my brown eye! john: Looks too much like your face.
[US]H. Rawson Dict. of Invective (1991) 53: To blow off [one’s] mouth is to talk too much.
in C. Reiser Reflections on Anger 66: I would blow off at the mouth, throw punches, grab, and apologize later.