Usage of the word suicide - validity of 'suiciding'
The reason the word is not often found as a verb, is that the -cide in suicide, like patricide, matricide, infanticide, fratricide, etc, is not a verb to start with, but a noun derived from a verb. Verbing does not seem to make a lot of sense.
etymonline says the following for -cide:
word-forming element meaning "killer," from French -cide, from Latin -cida "cutter, killer, slayer," from -cidere, comb. form of caedere "to strike down, chop, beat, hew, fell, slay," from PIE *kae-id-, from root *(s)k(h)ai- "to strike" (Pokorny, not in Watkins; cf. Sanskrit skhidati "beats, tears," Lithuanian kaisti "shave," German heien "beat"). For Latin vowel change, see acquisition. The element also can represent "killing," from French -cide, from Latin -cidium "a cutting, a killing.
If it is understood that -cide means killing or killer, it is not strange that it is not normally used as a verb.
However, users of English have a tendency of verbing their nouns, even if that may not go down well with many other speakers.
In this case, the verbing of suicide would be similar to verbing "killer" as "I killered you" or possibly "a killing" as "I killinged you".
It certainly explains WS2's reaction, and honestly, I would use it either. Since dictionaries record how language is used, and since (sadly?) enough people have no scruples about "killering", it has become an established (if marginally) verb, at least according to Merriam-Webster.
That a verb is in a dictionary does not mean you are obliged to use it though! :)
Having been one who made an early caustic comment on this matter, and notwithstanding @oerkelens well articulated and informed answer, above; I feel bound to mention that the OED points to a long tradition of 'suicide' having been used as a verb, dating from 1840. See below, including the gruesome ironic twist in the second section. Etymology: < suicide n.2 Compare French se suicider. Thesaurus »
- intr. and refl. To commit suicide.
1840 C. J. Lever Charles O'Malley xxxii, in Dublin Univ. Mag. Sept. 354/2 Here was I enacting Romeo for three mortal days.., soliloquising, half-suiciding.
1847 J. W. Carlyle Lett. & Mem. (1883) II. 18 The expediency..of suiciding myself is no longer a question with me.
- trans. (euphemistically) To do to death.
1876 Spectator 12 Aug. 997 in N. & Q., As the Divan cannot pass over the next heir..and as it is difficult to suicide him [etc.].
1898 Daily News 17 Oct. 4/5 The actual forger was, to use a convenient piece of French slang, ‘suicided’ in gaol.