  This paper discusses a model where a violent periastron collision of stars in
an eccentric binary system induces an eruption or explosion seen as a brief
transient source, attributed to LBVs, SN impostors, or other transients. The
key ingredient is that an evolved primary increases its photospheric radius on
relatively short timescales, to a point where the radius is comparable to or
larger than the periastron separation in an eccentric binary. In such a
configuration, a violent and sudden collision would ensue, possibly leading to
substantial mass ejection instead of a binary merger. Repeated periastral
grazings in an eccentric system could quickly escalate to a catastrophic
encounter, wherein the companion star actually plunges deep inside the
photosphere of a bloated primary during periastron, as a result of the primary
star increasing its own radius. This is motivated by the case of $\eta$
Carinae, where such a collision must have occured if conventional estimates of
the present-day orbit are correct, and where brief peaks in the light curve
coincide with periastron. Stellar collisions may explain brief recurring LBV
outbursts like SN 2000ch and SN 2009ip, and perhaps outbursts from relatively
low-mass progenitor stars (collisons are not necessarily the exclusive domain
of very luminous stars). Finally, mass ejections induced repeatedly at
periastron cause orbital evolution; this may explain the origin of very
eccentric colliding-wind Wolf-Rayet binaries such as WR140.
